Minnesota

Tree Inspector

Certification

Study Packet

Minnesota Department of Natural Resources

Division of Forestry

500 Lafayette Road Box 44

St Paul MN 55155

651-259-5300

Revised for 2012

Please use the enclosed publications to prepare for the Certified Tree Inspector examination

How to Identify and Manage Dutch Elm Disease by Haugen

Management of Dutch Elm Disease by David French (from History of DED in MN)

The Future for Elms in Minnesota by David French (from History of DED in MN)

Oak Wilt in Minnesota by French and Juzwik

Root Graft Control Barriers for Oak Wilt Control (MDA)

Oak Wilt Versus Dutch Elm Disease Control (MDA)

Oak Wilt and Dutch Elm Disease Control Timetables (UMN)

Emerald Ash Borer by Jeff Hahn

Pest Alert Forest Tent Caterpillar (USFS)

Pest Alert Bur Oak Blight (USFS)

American and Oriental Bittersweet Identification (USGS)

Pest Alert Thousand Canker Disease (USFS)

Supplemental Materials

Materials included based on availability

Gypsy Moth (MDA)

Whatrsquos In That Wood Pile by Johnson and Koetter

Best Management Practices for Known EAB infested areas (MDA)

Emerald Ash Borer (MDA USFS UMN Extension DNR)

Identify and Manage Dutch Elm Disease

Author Linda Haugen is a Plant Pathologist with the USDA Forest Service Northeastern Area State and Private Forestry St Paul Minnesota

Acknowledgments Thanks are extended to the many scientists who contributed suggestions and background material for this publication Particular thanks for review of technical content go to Mark Stennes Consulting arborist Top Notch Tree Care Dr Jay Stipes Professor of Plant Pathology Virginia Polytechnic Institute and State University Dr Eugene Smalley Emeritus Professor of Plant Pathology University of Wisconsin-Madison Dr Alden Townsend Research Geneticist USDA National Arboretum James Sherald Plant Pathologist National Park Service and Dr Richard Campana Emeritus Professor of Plant Pathology University of Maine Thanks for review of practical content are extended to Jim Hermann of Minneapolis Park and Recreation Board for review of the manuscript

Cover photo Branch flagging symptoms from a single point of Dutch elm disease infection in crown of elm (Photo courtesy of Dr R Jay Stipes)

The use of trade of firm names in this publication is for reader information and does not imply endorsement by the US Department of Agriculture of any product or service

Contents

bull Introduction bull Symptoms bull Distinguishing Dutch Elm Disease

from other problems bull Disease Cycle of Dutch Elm Disease bull Managing Dutch Elm Disease bull Trees in Natural Stands and Wild Areas bull Deciding Which Management Practices to Use bull Bibliography

Introduction

At one time the American elm was considered to be an ideal street tree because it was graceful long-lived fast growing and tolerant of compacted soils and air pollution Then Dutch elm disease (DED) was introduced and began devastating the elm population Estimates of DED losses of elm in communities and woodlands across the US are staggering (figure 1) Because elm is so well-suited to urban environments it continues to be a valued component of the urban forest despite the losses from DED The challenge before us is to reduce the loss of remaining elms and to choose suitable replacement trees for the ones we cannot save

This guide provides an update for urban foresters and tree care specialists with the latest information and management options available for Dutch elm disease

Figure 1 This photo is all too typical of the devastation caused by Dutch elm disease Once a tree in a row is infected the disease can move through connected root systems to kill the entire row (Photo courtesy of USDA Forest Service via Dr R Jay Stipes Virginia Polytechnic Institute and State University)

Symptoms

DED symptoms are the result of a fungus infecting the vascular (water conducting) system of the tree Infection by the fungus results in clogging of vascular tissues preventing water movement to the crown and causing visual symptoms as the tree wilts and dies

Foliage symptoms Symptoms of DED begin as wilting of leaves and proceed to yellowing and browning The pattern of symptom progression within the crown varies depending on where the fungus is introduced to the tree If the fungus enters the tree through roots grafted to infected trees (see disease cycle section) the symptoms may begin in the lower crown on the side nearest the graft and the entire crown may be affected very rapidly If infection begins in the upper crown symptoms often first appear at the end of an individual branch (called flagging) and progress downward in the crown (cover photo)

Multiple branches may be individually infected resulting in symptom development at several locations in the crown (figure 2) Symptoms begin in late spring or any time later during the growing season However if the tree was infected the previous year (and not detected) symptoms may first be observed in early spring Symptoms may progress throughout the whole tree in a single season or may take two or more years

Figure 2 Branch death or Flagging at multiple locations in the crown of a diseased elm (Photo courtesy of Dr Steve KatovichUSDA Forest Service St PaulMN)

Vascular symptoms Branches and stems of elms infected by the DED fungus typically develop dark streaks of discoloration To detect discoloration cut through and peel off the bark of a dying branch to expose the outer rings of wood In newly infected branches brown streaks characteristically appear in the sapwood of the current year (figure 3) It is important to cut deeply into the wood or look at the branch in cross section for two reasons (1) As the season progresses the staining may be overlaid by unstained wood and (2) if infection occurred in the previous year the current sapwood may not be discolored

Figure 3 Brown streaking develops in sapwood of branches infected by Dutch elm disease fungus Streaking is visible here (from left to right) in (1) the newly formed sapwood (2) spring sapwood overlaid by uninfected summer wood and (3) is absent in an uninfected branch (Photo courtesy of the America Phytopathological Society)

Distinguishing Dutch Elm Disease From Other Problems

Other pest problems commonly observed on elm include leaf spot diseases which cause dark spots of dead tissue in the leaves and elm leaf beetles which eat holes in the leaves These problems are easily distinguished from DED Elm leaf beetles do not carry the Dutch elm disease fungus as elm bark beetles do

Two other diseases elm yellows and bacterial leaf scorch are more easily confused with DED The symptoms of these diseases are compared to DED in table 1

Elm yellows This disease which is also called elm phloem necrosis is caused by a phytoplasma (microscopic bacteria-like organism) which systemically infects the phloem tissue (inner bark) of the tree It is a serious disease that causes tree death Symptoms of elm yellows differ from DED in that the leaves turn yellow (not brown and wilted) and drop prematurely and the symptoms appear in the entire crown at the same time The brown streaking which DED causes in the sapwood is absent but the inner bark develops a tan discoloration and a characteristic wintergreen odor

Bacterial leaf scorch This disease is caused by the bacterium Xylella fastidiosa which infects and clogs the water conducting tissues of the tree Infection by this bacterium causes a slow decline over many years Once a tree is infected symptoms recur annually Symptoms of scorch are irregular browning along the leaf margin with a yellow border between green and scorched leaf tissue Older leaves on a branch are affected first Disease Cycle of Dutch Elm Disease

The biology or disease cycle of DED depends upon the host the fungus and the means by which the fungus moves into new host trees (figure 4)

Figure 4 The disease cycle of Dutch elm disease is closely linked to the life cycle of elm bark beetles

(Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The elm host Native species of North American elms vary in their susceptibility to DED even within species American elm (Ulmus americana L) is generally highly susceptible Winged elm (U alata Michx) September elm (U serotina Sarg) slippery elm (U rubra Muhl) rock elm (U thomasii Sarg) and cedar elm (U crassifolia Nutt) range from susceptible to somewhat resistant No native elms are immune to DED but some individuals or cultivars have a higher tolerance (and thus may recover from or survive with infection) or resistance to DED Many European and Asiatic elms are less susceptible than American elm

In addition to genetic factors present in some cultivars and species physical factors affect tree susceptibility These factors include time of year climatic conditions (such as drought) and vitality of the tree Water conducting elements are most susceptible to infection as they are being produced in the spring thus elms are most susceptible to infection after earliest leafing out to midsummer Trees are less susceptible under drought conditions Vigorously growing trees are generally more susceptible than slower growing trees

The Dutch elm disease fungus DED can be caused by either of two closely related species of fungi Ophiostoma ulmi (Buism) Nannf (formerly called Ceratocystis ulmi) and Ophiostoma novo-ulmi Brasier The latter which is more aggressive in causing disease was recently recognized as being a separate species The DED fungus was first introduced to the US on diseased elm logs from Europe prior to 1930 It is unknown when the more aggressive species became established in the US however it was possibly present as early as the 1940s- 1950s and most likely caused much of the devastating mortality through the 1970s The less aggressive species is becoming increasingly rare in nature and the aggressive species is thought to be responsible for most of the current mortality Although some local resurgence of DED has been observed there is no evidence that it is due to a change in the pathogen Localized resurgence is more likely due to the following (1) a decrease in vigilance in monitoring and sanitation (2) a build-up in populations of the insect vectors or (3) ingrowth of susceptible host trees in the wild

Spread by elm bark beetles Overland spread of DED is closely linked to the life cycles of the native elm bark beetle (Hylurgopinus rufipes Eich) and the smaller European elm bark beetle (Scolytus multistriatus Marsh) (figure 5) Both beetles are attracted to stressed dying or dead elm wood to complete the breeding stage of their life cycle The adult beetles tunnel into the bark and lay their eggs in tunnels (called galleries) in the inner bark The eggs hatch and the larvae feed in the inner bark and sapwood

The larvae mature into adults and emerge from the elm wood If the DED fungus was present in the wood that the beetles infested the fungus produces sticky spores in the beetle galleries Spores of the DED fungus are eaten by or stick to the adult beetles as they emerge from diseased trees Adult beetles then visit healthy trees feed in twig crotches or branch inner bark and introduce the fungus into or near severed wood vessels as they feed

Figure 5 Overland spread of DED is closely tied to the life cycles of the Native elm bark beetle (top) and smaller European elm bark beetle (below) Note that the smaller European elm bark beetle is actually larger

than the native elm bark beetle (Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The importance of the two bark beetle species as vectors of DED varies across the range of elms In northern areas (northern parts of Minnesota Wisconsin Maine New York and New England and most of Canada where winter temperatures below -6deg F are common) the native elm bark beetle is the predominant vector In other parts of North America the smaller European elm bark beetle predominates The life habits of the adults of the two species differ considerably which has implications for management opportunities These differences are described below

Smaller European elm bark beetles overwinter as larvae or adults within the stem of the tree where they hatched They emerge as adults in spring to feed in twig crotches of healthy trees where they can introduce spores of the DED fungus to the crown High numbers of beetles frequently will feed in a single tree resulting in multiple points of infection The cycle is repeated when beetles then seek out diseased and dying wood to breed in throughout the growing season completing two or more generations per year They have the potential to rapidly build up high populations

Adult native elm bark beetles tunnel into the bark on the lower stems of healthy elms to overwinter In spring they emerge to feed in the inner bark of elm branches and small stems before beginning their breeding cycle They repeat their life cycle as previously described They can transmit the DED fungus to healthy trees during the construction of overwintering sites in fall or more commonly during feeding in spring

Once the DED fungus is introduced into the upper crown of healthy elms by bark beetles it slowly moves downward killing the

branch as it goes Disease progression may occur rapidly killing the tree by the end of the growing season or may progress gradually over a period of two or more years It is also possible that the tree may recover The success and rate of progression within the tree depends on tree size time and location of infection in the tree climatic conditions and response of the host tree Spread through grafted roots Roots of the same or closely related tree species growing near each other often cross each other in the soil and eventually fuse (become grafted) to each other

The DED fungus can move from infected trees to adjacent trees through these grafted roots Infections that occur through root grafts can spread very rapidly throughout the tree as the fungus is carried upward in the sapstream Root graft spread of DED is a very significant cause of tree death in urban areas where elms are closely spaced (figure 6)

Figure 6 Where elms are closely spaced the Dutch elm disease fungus may move down a row of trees through grafted roots Removing trees without breaking root grafts may not keep the fungus from moving into adjacent trees (Photo courtesy of Dr Joseph OBrien USDA Forest Service St Paul MN)

Managing Dutch Elm Disease

DED is managed by interrupting the disease cycle The most effective means of breaking the cycle is early and thorough sanitation to limit the population of the insects that transmit the fungus from tree to tree Other useful means of affecting the disease cycle include using insecticides to kill the insect vector breaking root grafts between trees injecting individual trees with fungicides to prevent or halt the fungus pruning out early infections and planting DED tolerant or resistant elm cultivars or other tree species

Sanitation to reduce insect vectors Many communities have been able to maintain a healthy population of mature elms through a vigilant program of identification and removal of diseased elms and systematic pruning of weakened dying or dead branches Sanitation by prompt removal of diseased trees or branches reduces breeding sites for elm bark beetles and eliminates the source of the DED fungus To be completely effective in interrupting the spread of the disease by elm bark beetles stems and branches of DED infected trees must be de-barked destroyed or utilized before the bark beetles emerge During the growing season removal should be completed within 2 to 3 weeks of detection During the dormant season removal should be completed before April when overwintering beetles may begin to emerge

Wood from infected trees can be destroyed by chipping burning or burying Wood may be retained for use as firewood or sawlogs if it is de-barked or covered from April 15th to October 15th with 4 to 6 mil plastic The edges of the cover must be buried or sealed to the ground If it is impossible to destroy all elm wood before the beetles emerge the wood can be sprayed with a registered insecticide until disposal is possible If insecticides are used consider potential exposure to chemical residues when burning or handling the treated wood Many communities have regulations on the removal of diseased elms and storage of elm firewood make sure your activities comply with local regulations

Insecticides to kill insect vectors In areas where the native elm bark beetle is the principal vector sanitation may be augmented by applying a registered insecticide to the lower stem of healthy elms in late summer to early fall (ie at the first sign of autumn leaf color change) to kill adult beetles as they prepare overwintering sites In areas where the smaller European elm bark beetle are common spring feeding in twig crotches can be prevented by spraying the crowns of elm trees with a registered insecticide However this may not be a preferred treatment method because of the difficulty in getting thorough coverage of all susceptible twig tissue the risk of insecticide drift and exposure and high expense

Insecticide registrations and recommendations are frequently updated and may vary considerably between states Cooperative Extension Services at land grant colleges and certified arborists are able to provide current insecticide recommendations

Disruption of root grafts Large trees within 25 to 50 feet of each other are likely to have root grafts Breaking root grafts between infected trees and adjacent healthy trees is an important means to prevent movement of the fungus into the healthy trees Root grafts should also be disrupted between the healthy tree adjacent to a diseased tree and the next healthy tree It may even be desirable to sever grafts between very valuable trees before DED is observed in the vicinity as a proactive measure

Root graft disruption should be completed before the infected trees are removed Otherwise the transpirational pull from healthy trees will rapidly draw in the contents of diseased trees root system when the vascular tension on the roots of the diseased tree is released by severing the stem Root graft disruption can be accomplished by use of a vibratory plow or any trenching machine equipped with the longest blade available (preferably five-feet long but at least three-feet long) Biocidal soil fumigants may also be used to kill root

grafts if no other alternatives are available However these chemicals are generally restricted use pesticides and may only be applied by professional pesticide applicators In addition biocidal chemicals may not be effective if soil temperatures are below 50 degF Injecting elms with fungicide Certain fungicides when properly injected are effective in protecting elm trees from infection via beetle transmission This treatment is expensive and must be repeated every one to three seasons thus it is appropriate only for high value or historically important trees The treatment itself also may pose risks to the health of the tree

Figure 7

Macroinjection of fungicide into the root flare of an elm tree (Photo courtesy of Mark Stennes certified arborist St Paul MN)

In order to be effective the fungicide must be present at adequate concentration at all potential points of infection Thus the dosage and means of application are critical to success The injection of chemical into root flares in large volumes of water (macroinjection) provides thorough distribution of chemical in the crown (figure 7) Microinjection (injection of small volumes of concentrated chemical) is also an option although its efficacy compared to macroinjection has not been thoroughly researched Preferably injections should be done soon after the earliest leaves have fully expanded but may be done from then to the end of the growing season Label rates of concentration for chemical application are updated to reflect the most recent findings on effectiveness always follow the current label

Harmful effects of fungicide injection have sometimes been reported and include occasional leaf scorching or loss Elms generally recover from this damage Also drilling injection holes results in wounding which if repeated annually may eventually result in significant discoloration and decay Following fungicide injection with a flush of clean water can reduce damage to the cambium Some chemicals are able to protect trees for up to three seasons thus minimizing the frequency of treatments

Several fungicides are registered for injection to prevent DED infection These chemicals vary in duration of protective effects means of application risk of damage to the tree documentation of effectiveness and cost Certified arborists or Cooperative Extension Services at land grant colleges are able to provide current recommendations on product availability and effectiveness Eradicating Dutch elm disease from newly infected trees If a new crown infection of DED is detected early enough there is opportunity to save a tree through pruning fungicide injection or both Eradicative treatment is not possible on trees that have become infected via root graft transmission Pruning which can literally eradicate the fungus from the tree by removing it has a high probability of saving a newly infected tree that has less than 5 of its crown affected To be a candidate for eradicative pruning the infection must be a new infection (not a residual infection from the previous season) and be present only in the upper crown (not yet present in the main stem) Since infection may be more advanced than symptoms indicate it is important to peel off the bark of infected branches and locate the staining which indicates the presence of the fungus All infected branches should be removed at a branch fork at least 5 feet and preferably 10 feet below the last sign of streaking in the sapwood (figure 8) Whenever elm branches are pruned during the growing season pruning paint specifically formulated for use on trees should be applied to prevent attraction of elm bark beetles to the wounded trees (Painting tree wounds is generally not recommended except to prevent disease transmission in oaks and elms)

Figure 8 Eradicative pruning of branches infected with DED may be effective if there is adequate length (5 to 10 feet) of clearwood between the infected tissue and the remainder of the crown or if the tree has been properly treated with fungicide (Artwork courtesy of Jim Lockyer USDA Forest Service Radnor PA)

Pruning is more likely to be effective if augmented by systemic injection of fungicides Proper use of fungicides eliminates the need to eradicate all infected tissues from the tree although all dead branches should eventually be removed Whereas pruning alone is not effective against residual infections fungicide injection may be If fungicides are used they should be injected prior to removal of diseased branches The keys to successful eradicative treatment are early detection and prompt treatment

Planting Dutch Elm Disease resistant or tolerant trees Planting trees with resistance or tolerance to DED is a valid management option However selecting only a few cultivars limits the genetic variability of the population This could lead to increased risk of widespread losses if these cultivars are found to be susceptible to tree health problems such as poor adaptation to site air pollution other elm pests or pathogens (such as elm yellows or elm leaf beetle) or even other strains of DED which may eventually develop Thus it is prudent to plant a mixture of suitable cultivars of as many elm genotypes as possible Santamour and Bentz (1995) recently published a checklist and brief description of elm cultivars in North America The only true American elms on that list that are commercially available and have strong evidence of DED tolerance or resistance are the Princeton Elm the American Liberty multi-clone and Independence which is one of the cultivars in the American Liberty multi-clone Two additional American elms Valley Forge and New Harmony were released by the USDA National Arboretum since the Santamour and Bentz listing was prepared These two cultivars which exhibit high tolerance to DED should be available through retail nurseries by 2001

Besides true American elms there are many other hybrid elm crosses and species of elm that have high tolerance or resistance to DED Several of these have attractive form are well suited to urban environments and are readily available (figure 9) Many of these are listed and described by Santamour and Bentz (1995) in the previously mentioned checklist

Figure 9 Cultivars of elm selected for resistance to DED are available This selection of Ulmus japonica demonstrates the potential these elms have as landscape trees (Photo courtesy of Dr Eugene Smalley University of Wisconsin--Madison)

In addition to careful selection of the tree species and cultivar location and spacing are also important to reduce losses from DED When selecting landscape trees and their locations plant a mixture of tree species appropriate to the site In addition to the species diversity consider spacing of the trees Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity

Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and DED fungus to infect high value landscape trees Management is necessary in order to protect urban elms

The most effective management option to reduce both the bark beetle vectors and the DED fungus is sanitation to promptly remove stressed dead and dying elms as previously described However this intensity of treatment is often not feasible

A trap tree method was developed in the 1980s to more cost effectively reduce populations of elm bark beetles Under this method DED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark The bark beetles are attracted to the dying trees but the rapidly drying bark is unsuitable for them to complete their lifecycle and the bark beetle populations are reduced However treated trees may then become hazard trees with high risk of falling and causing personal injury or property damage

Another option in wild areas or natural stands other than accepting losses from DED is to eliminate all elms and manage for alternative species However it is often desirable to retain elms for biodiversity aesthetic economic or other reasons

Deciding Which Management Practices to Use Different management strategies will be applicable depending on whether you are working with a community program or trying to protect individual trees In a community program the objective will be to protect a population of elms Individual landowners however may have no control over what neighbors do with their elms but may want to protect or save their own trees The amount of money an individual or community is able to spend will also vary

Where you have no control over the management of surrounding trees the only options available are treatments to protect or save individual trees Good sanitation practices and disruption of root grafts are necessary on individual properties but these practices alone will not protect a tree from disease transmission by bark beetles from other properties Preventive fungicide injection eradicative pruning and fungicide injection and insecticide treatment are generally the only options available for individual trees

In a community program resources to spend on individual trees may be low but there is more opportunity to manage populations of elms Where there are continuous elms root graft disruption is essential to halt the spread Sanitation is key to reducing beetle and DED populations and is effective Community ordinances can be established to encourage prompt removal of diseased trees and

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Please use the enclosed publications to prepare for the Certified Tree Inspector examination

How to Identify and Manage Dutch Elm Disease by Haugen

Management of Dutch Elm Disease by David French (from History of DED in MN)

The Future for Elms in Minnesota by David French (from History of DED in MN)

Oak Wilt in Minnesota by French and Juzwik

Root Graft Control Barriers for Oak Wilt Control (MDA)

Oak Wilt Versus Dutch Elm Disease Control (MDA)

Oak Wilt and Dutch Elm Disease Control Timetables (UMN)

Emerald Ash Borer by Jeff Hahn

Pest Alert Forest Tent Caterpillar (USFS)

Pest Alert Bur Oak Blight (USFS)

American and Oriental Bittersweet Identification (USGS)

Pest Alert Thousand Canker Disease (USFS)

Supplemental Materials

Materials included based on availability

Gypsy Moth (MDA)

Whatrsquos In That Wood Pile by Johnson and Koetter

Best Management Practices for Known EAB infested areas (MDA)

Emerald Ash Borer (MDA USFS UMN Extension DNR)

Identify and Manage Dutch Elm Disease

Author Linda Haugen is a Plant Pathologist with the USDA Forest Service Northeastern Area State and Private Forestry St Paul Minnesota

Acknowledgments Thanks are extended to the many scientists who contributed suggestions and background material for this publication Particular thanks for review of technical content go to Mark Stennes Consulting arborist Top Notch Tree Care Dr Jay Stipes Professor of Plant Pathology Virginia Polytechnic Institute and State University Dr Eugene Smalley Emeritus Professor of Plant Pathology University of Wisconsin-Madison Dr Alden Townsend Research Geneticist USDA National Arboretum James Sherald Plant Pathologist National Park Service and Dr Richard Campana Emeritus Professor of Plant Pathology University of Maine Thanks for review of practical content are extended to Jim Hermann of Minneapolis Park and Recreation Board for review of the manuscript

Cover photo Branch flagging symptoms from a single point of Dutch elm disease infection in crown of elm (Photo courtesy of Dr R Jay Stipes)

The use of trade of firm names in this publication is for reader information and does not imply endorsement by the US Department of Agriculture of any product or service

Contents

bull Introduction bull Symptoms bull Distinguishing Dutch Elm Disease

from other problems bull Disease Cycle of Dutch Elm Disease bull Managing Dutch Elm Disease bull Trees in Natural Stands and Wild Areas bull Deciding Which Management Practices to Use bull Bibliography

Introduction

At one time the American elm was considered to be an ideal street tree because it was graceful long-lived fast growing and tolerant of compacted soils and air pollution Then Dutch elm disease (DED) was introduced and began devastating the elm population Estimates of DED losses of elm in communities and woodlands across the US are staggering (figure 1) Because elm is so well-suited to urban environments it continues to be a valued component of the urban forest despite the losses from DED The challenge before us is to reduce the loss of remaining elms and to choose suitable replacement trees for the ones we cannot save

This guide provides an update for urban foresters and tree care specialists with the latest information and management options available for Dutch elm disease

Figure 1 This photo is all too typical of the devastation caused by Dutch elm disease Once a tree in a row is infected the disease can move through connected root systems to kill the entire row (Photo courtesy of USDA Forest Service via Dr R Jay Stipes Virginia Polytechnic Institute and State University)

Symptoms

DED symptoms are the result of a fungus infecting the vascular (water conducting) system of the tree Infection by the fungus results in clogging of vascular tissues preventing water movement to the crown and causing visual symptoms as the tree wilts and dies

Foliage symptoms Symptoms of DED begin as wilting of leaves and proceed to yellowing and browning The pattern of symptom progression within the crown varies depending on where the fungus is introduced to the tree If the fungus enters the tree through roots grafted to infected trees (see disease cycle section) the symptoms may begin in the lower crown on the side nearest the graft and the entire crown may be affected very rapidly If infection begins in the upper crown symptoms often first appear at the end of an individual branch (called flagging) and progress downward in the crown (cover photo)

Multiple branches may be individually infected resulting in symptom development at several locations in the crown (figure 2) Symptoms begin in late spring or any time later during the growing season However if the tree was infected the previous year (and not detected) symptoms may first be observed in early spring Symptoms may progress throughout the whole tree in a single season or may take two or more years

Figure 2 Branch death or Flagging at multiple locations in the crown of a diseased elm (Photo courtesy of Dr Steve KatovichUSDA Forest Service St PaulMN)

Vascular symptoms Branches and stems of elms infected by the DED fungus typically develop dark streaks of discoloration To detect discoloration cut through and peel off the bark of a dying branch to expose the outer rings of wood In newly infected branches brown streaks characteristically appear in the sapwood of the current year (figure 3) It is important to cut deeply into the wood or look at the branch in cross section for two reasons (1) As the season progresses the staining may be overlaid by unstained wood and (2) if infection occurred in the previous year the current sapwood may not be discolored

Figure 3 Brown streaking develops in sapwood of branches infected by Dutch elm disease fungus Streaking is visible here (from left to right) in (1) the newly formed sapwood (2) spring sapwood overlaid by uninfected summer wood and (3) is absent in an uninfected branch (Photo courtesy of the America Phytopathological Society)

Distinguishing Dutch Elm Disease From Other Problems

Other pest problems commonly observed on elm include leaf spot diseases which cause dark spots of dead tissue in the leaves and elm leaf beetles which eat holes in the leaves These problems are easily distinguished from DED Elm leaf beetles do not carry the Dutch elm disease fungus as elm bark beetles do

Two other diseases elm yellows and bacterial leaf scorch are more easily confused with DED The symptoms of these diseases are compared to DED in table 1

Elm yellows This disease which is also called elm phloem necrosis is caused by a phytoplasma (microscopic bacteria-like organism) which systemically infects the phloem tissue (inner bark) of the tree It is a serious disease that causes tree death Symptoms of elm yellows differ from DED in that the leaves turn yellow (not brown and wilted) and drop prematurely and the symptoms appear in the entire crown at the same time The brown streaking which DED causes in the sapwood is absent but the inner bark develops a tan discoloration and a characteristic wintergreen odor

Bacterial leaf scorch This disease is caused by the bacterium Xylella fastidiosa which infects and clogs the water conducting tissues of the tree Infection by this bacterium causes a slow decline over many years Once a tree is infected symptoms recur annually Symptoms of scorch are irregular browning along the leaf margin with a yellow border between green and scorched leaf tissue Older leaves on a branch are affected first Disease Cycle of Dutch Elm Disease

The biology or disease cycle of DED depends upon the host the fungus and the means by which the fungus moves into new host trees (figure 4)

Figure 4 The disease cycle of Dutch elm disease is closely linked to the life cycle of elm bark beetles

(Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The elm host Native species of North American elms vary in their susceptibility to DED even within species American elm (Ulmus americana L) is generally highly susceptible Winged elm (U alata Michx) September elm (U serotina Sarg) slippery elm (U rubra Muhl) rock elm (U thomasii Sarg) and cedar elm (U crassifolia Nutt) range from susceptible to somewhat resistant No native elms are immune to DED but some individuals or cultivars have a higher tolerance (and thus may recover from or survive with infection) or resistance to DED Many European and Asiatic elms are less susceptible than American elm

In addition to genetic factors present in some cultivars and species physical factors affect tree susceptibility These factors include time of year climatic conditions (such as drought) and vitality of the tree Water conducting elements are most susceptible to infection as they are being produced in the spring thus elms are most susceptible to infection after earliest leafing out to midsummer Trees are less susceptible under drought conditions Vigorously growing trees are generally more susceptible than slower growing trees

The Dutch elm disease fungus DED can be caused by either of two closely related species of fungi Ophiostoma ulmi (Buism) Nannf (formerly called Ceratocystis ulmi) and Ophiostoma novo-ulmi Brasier The latter which is more aggressive in causing disease was recently recognized as being a separate species The DED fungus was first introduced to the US on diseased elm logs from Europe prior to 1930 It is unknown when the more aggressive species became established in the US however it was possibly present as early as the 1940s- 1950s and most likely caused much of the devastating mortality through the 1970s The less aggressive species is becoming increasingly rare in nature and the aggressive species is thought to be responsible for most of the current mortality Although some local resurgence of DED has been observed there is no evidence that it is due to a change in the pathogen Localized resurgence is more likely due to the following (1) a decrease in vigilance in monitoring and sanitation (2) a build-up in populations of the insect vectors or (3) ingrowth of susceptible host trees in the wild

Spread by elm bark beetles Overland spread of DED is closely linked to the life cycles of the native elm bark beetle (Hylurgopinus rufipes Eich) and the smaller European elm bark beetle (Scolytus multistriatus Marsh) (figure 5) Both beetles are attracted to stressed dying or dead elm wood to complete the breeding stage of their life cycle The adult beetles tunnel into the bark and lay their eggs in tunnels (called galleries) in the inner bark The eggs hatch and the larvae feed in the inner bark and sapwood

The larvae mature into adults and emerge from the elm wood If the DED fungus was present in the wood that the beetles infested the fungus produces sticky spores in the beetle galleries Spores of the DED fungus are eaten by or stick to the adult beetles as they emerge from diseased trees Adult beetles then visit healthy trees feed in twig crotches or branch inner bark and introduce the fungus into or near severed wood vessels as they feed

Figure 5 Overland spread of DED is closely tied to the life cycles of the Native elm bark beetle (top) and smaller European elm bark beetle (below) Note that the smaller European elm bark beetle is actually larger

than the native elm bark beetle (Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The importance of the two bark beetle species as vectors of DED varies across the range of elms In northern areas (northern parts of Minnesota Wisconsin Maine New York and New England and most of Canada where winter temperatures below -6deg F are common) the native elm bark beetle is the predominant vector In other parts of North America the smaller European elm bark beetle predominates The life habits of the adults of the two species differ considerably which has implications for management opportunities These differences are described below

Smaller European elm bark beetles overwinter as larvae or adults within the stem of the tree where they hatched They emerge as adults in spring to feed in twig crotches of healthy trees where they can introduce spores of the DED fungus to the crown High numbers of beetles frequently will feed in a single tree resulting in multiple points of infection The cycle is repeated when beetles then seek out diseased and dying wood to breed in throughout the growing season completing two or more generations per year They have the potential to rapidly build up high populations

Adult native elm bark beetles tunnel into the bark on the lower stems of healthy elms to overwinter In spring they emerge to feed in the inner bark of elm branches and small stems before beginning their breeding cycle They repeat their life cycle as previously described They can transmit the DED fungus to healthy trees during the construction of overwintering sites in fall or more commonly during feeding in spring

Once the DED fungus is introduced into the upper crown of healthy elms by bark beetles it slowly moves downward killing the

branch as it goes Disease progression may occur rapidly killing the tree by the end of the growing season or may progress gradually over a period of two or more years It is also possible that the tree may recover The success and rate of progression within the tree depends on tree size time and location of infection in the tree climatic conditions and response of the host tree Spread through grafted roots Roots of the same or closely related tree species growing near each other often cross each other in the soil and eventually fuse (become grafted) to each other

The DED fungus can move from infected trees to adjacent trees through these grafted roots Infections that occur through root grafts can spread very rapidly throughout the tree as the fungus is carried upward in the sapstream Root graft spread of DED is a very significant cause of tree death in urban areas where elms are closely spaced (figure 6)

Figure 6 Where elms are closely spaced the Dutch elm disease fungus may move down a row of trees through grafted roots Removing trees without breaking root grafts may not keep the fungus from moving into adjacent trees (Photo courtesy of Dr Joseph OBrien USDA Forest Service St Paul MN)

Managing Dutch Elm Disease

DED is managed by interrupting the disease cycle The most effective means of breaking the cycle is early and thorough sanitation to limit the population of the insects that transmit the fungus from tree to tree Other useful means of affecting the disease cycle include using insecticides to kill the insect vector breaking root grafts between trees injecting individual trees with fungicides to prevent or halt the fungus pruning out early infections and planting DED tolerant or resistant elm cultivars or other tree species

Sanitation to reduce insect vectors Many communities have been able to maintain a healthy population of mature elms through a vigilant program of identification and removal of diseased elms and systematic pruning of weakened dying or dead branches Sanitation by prompt removal of diseased trees or branches reduces breeding sites for elm bark beetles and eliminates the source of the DED fungus To be completely effective in interrupting the spread of the disease by elm bark beetles stems and branches of DED infected trees must be de-barked destroyed or utilized before the bark beetles emerge During the growing season removal should be completed within 2 to 3 weeks of detection During the dormant season removal should be completed before April when overwintering beetles may begin to emerge

Wood from infected trees can be destroyed by chipping burning or burying Wood may be retained for use as firewood or sawlogs if it is de-barked or covered from April 15th to October 15th with 4 to 6 mil plastic The edges of the cover must be buried or sealed to the ground If it is impossible to destroy all elm wood before the beetles emerge the wood can be sprayed with a registered insecticide until disposal is possible If insecticides are used consider potential exposure to chemical residues when burning or handling the treated wood Many communities have regulations on the removal of diseased elms and storage of elm firewood make sure your activities comply with local regulations

Insecticides to kill insect vectors In areas where the native elm bark beetle is the principal vector sanitation may be augmented by applying a registered insecticide to the lower stem of healthy elms in late summer to early fall (ie at the first sign of autumn leaf color change) to kill adult beetles as they prepare overwintering sites In areas where the smaller European elm bark beetle are common spring feeding in twig crotches can be prevented by spraying the crowns of elm trees with a registered insecticide However this may not be a preferred treatment method because of the difficulty in getting thorough coverage of all susceptible twig tissue the risk of insecticide drift and exposure and high expense

Insecticide registrations and recommendations are frequently updated and may vary considerably between states Cooperative Extension Services at land grant colleges and certified arborists are able to provide current insecticide recommendations

Disruption of root grafts Large trees within 25 to 50 feet of each other are likely to have root grafts Breaking root grafts between infected trees and adjacent healthy trees is an important means to prevent movement of the fungus into the healthy trees Root grafts should also be disrupted between the healthy tree adjacent to a diseased tree and the next healthy tree It may even be desirable to sever grafts between very valuable trees before DED is observed in the vicinity as a proactive measure

Root graft disruption should be completed before the infected trees are removed Otherwise the transpirational pull from healthy trees will rapidly draw in the contents of diseased trees root system when the vascular tension on the roots of the diseased tree is released by severing the stem Root graft disruption can be accomplished by use of a vibratory plow or any trenching machine equipped with the longest blade available (preferably five-feet long but at least three-feet long) Biocidal soil fumigants may also be used to kill root

grafts if no other alternatives are available However these chemicals are generally restricted use pesticides and may only be applied by professional pesticide applicators In addition biocidal chemicals may not be effective if soil temperatures are below 50 degF Injecting elms with fungicide Certain fungicides when properly injected are effective in protecting elm trees from infection via beetle transmission This treatment is expensive and must be repeated every one to three seasons thus it is appropriate only for high value or historically important trees The treatment itself also may pose risks to the health of the tree

Figure 7

Macroinjection of fungicide into the root flare of an elm tree (Photo courtesy of Mark Stennes certified arborist St Paul MN)

In order to be effective the fungicide must be present at adequate concentration at all potential points of infection Thus the dosage and means of application are critical to success The injection of chemical into root flares in large volumes of water (macroinjection) provides thorough distribution of chemical in the crown (figure 7) Microinjection (injection of small volumes of concentrated chemical) is also an option although its efficacy compared to macroinjection has not been thoroughly researched Preferably injections should be done soon after the earliest leaves have fully expanded but may be done from then to the end of the growing season Label rates of concentration for chemical application are updated to reflect the most recent findings on effectiveness always follow the current label

Harmful effects of fungicide injection have sometimes been reported and include occasional leaf scorching or loss Elms generally recover from this damage Also drilling injection holes results in wounding which if repeated annually may eventually result in significant discoloration and decay Following fungicide injection with a flush of clean water can reduce damage to the cambium Some chemicals are able to protect trees for up to three seasons thus minimizing the frequency of treatments

Several fungicides are registered for injection to prevent DED infection These chemicals vary in duration of protective effects means of application risk of damage to the tree documentation of effectiveness and cost Certified arborists or Cooperative Extension Services at land grant colleges are able to provide current recommendations on product availability and effectiveness Eradicating Dutch elm disease from newly infected trees If a new crown infection of DED is detected early enough there is opportunity to save a tree through pruning fungicide injection or both Eradicative treatment is not possible on trees that have become infected via root graft transmission Pruning which can literally eradicate the fungus from the tree by removing it has a high probability of saving a newly infected tree that has less than 5 of its crown affected To be a candidate for eradicative pruning the infection must be a new infection (not a residual infection from the previous season) and be present only in the upper crown (not yet present in the main stem) Since infection may be more advanced than symptoms indicate it is important to peel off the bark of infected branches and locate the staining which indicates the presence of the fungus All infected branches should be removed at a branch fork at least 5 feet and preferably 10 feet below the last sign of streaking in the sapwood (figure 8) Whenever elm branches are pruned during the growing season pruning paint specifically formulated for use on trees should be applied to prevent attraction of elm bark beetles to the wounded trees (Painting tree wounds is generally not recommended except to prevent disease transmission in oaks and elms)

Figure 8 Eradicative pruning of branches infected with DED may be effective if there is adequate length (5 to 10 feet) of clearwood between the infected tissue and the remainder of the crown or if the tree has been properly treated with fungicide (Artwork courtesy of Jim Lockyer USDA Forest Service Radnor PA)

Pruning is more likely to be effective if augmented by systemic injection of fungicides Proper use of fungicides eliminates the need to eradicate all infected tissues from the tree although all dead branches should eventually be removed Whereas pruning alone is not effective against residual infections fungicide injection may be If fungicides are used they should be injected prior to removal of diseased branches The keys to successful eradicative treatment are early detection and prompt treatment

Planting Dutch Elm Disease resistant or tolerant trees Planting trees with resistance or tolerance to DED is a valid management option However selecting only a few cultivars limits the genetic variability of the population This could lead to increased risk of widespread losses if these cultivars are found to be susceptible to tree health problems such as poor adaptation to site air pollution other elm pests or pathogens (such as elm yellows or elm leaf beetle) or even other strains of DED which may eventually develop Thus it is prudent to plant a mixture of suitable cultivars of as many elm genotypes as possible Santamour and Bentz (1995) recently published a checklist and brief description of elm cultivars in North America The only true American elms on that list that are commercially available and have strong evidence of DED tolerance or resistance are the Princeton Elm the American Liberty multi-clone and Independence which is one of the cultivars in the American Liberty multi-clone Two additional American elms Valley Forge and New Harmony were released by the USDA National Arboretum since the Santamour and Bentz listing was prepared These two cultivars which exhibit high tolerance to DED should be available through retail nurseries by 2001

Besides true American elms there are many other hybrid elm crosses and species of elm that have high tolerance or resistance to DED Several of these have attractive form are well suited to urban environments and are readily available (figure 9) Many of these are listed and described by Santamour and Bentz (1995) in the previously mentioned checklist

Figure 9 Cultivars of elm selected for resistance to DED are available This selection of Ulmus japonica demonstrates the potential these elms have as landscape trees (Photo courtesy of Dr Eugene Smalley University of Wisconsin--Madison)

In addition to careful selection of the tree species and cultivar location and spacing are also important to reduce losses from DED When selecting landscape trees and their locations plant a mixture of tree species appropriate to the site In addition to the species diversity consider spacing of the trees Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity

Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and DED fungus to infect high value landscape trees Management is necessary in order to protect urban elms

The most effective management option to reduce both the bark beetle vectors and the DED fungus is sanitation to promptly remove stressed dead and dying elms as previously described However this intensity of treatment is often not feasible

A trap tree method was developed in the 1980s to more cost effectively reduce populations of elm bark beetles Under this method DED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark The bark beetles are attracted to the dying trees but the rapidly drying bark is unsuitable for them to complete their lifecycle and the bark beetle populations are reduced However treated trees may then become hazard trees with high risk of falling and causing personal injury or property damage

Another option in wild areas or natural stands other than accepting losses from DED is to eliminate all elms and manage for alternative species However it is often desirable to retain elms for biodiversity aesthetic economic or other reasons

Deciding Which Management Practices to Use Different management strategies will be applicable depending on whether you are working with a community program or trying to protect individual trees In a community program the objective will be to protect a population of elms Individual landowners however may have no control over what neighbors do with their elms but may want to protect or save their own trees The amount of money an individual or community is able to spend will also vary

Where you have no control over the management of surrounding trees the only options available are treatments to protect or save individual trees Good sanitation practices and disruption of root grafts are necessary on individual properties but these practices alone will not protect a tree from disease transmission by bark beetles from other properties Preventive fungicide injection eradicative pruning and fungicide injection and insecticide treatment are generally the only options available for individual trees

In a community program resources to spend on individual trees may be low but there is more opportunity to manage populations of elms Where there are continuous elms root graft disruption is essential to halt the spread Sanitation is key to reducing beetle and DED populations and is effective Community ordinances can be established to encourage prompt removal of diseased trees and

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Identify and Manage Dutch Elm Disease

Author Linda Haugen is a Plant Pathologist with the USDA Forest Service Northeastern Area State and Private Forestry St Paul Minnesota

Acknowledgments Thanks are extended to the many scientists who contributed suggestions and background material for this publication Particular thanks for review of technical content go to Mark Stennes Consulting arborist Top Notch Tree Care Dr Jay Stipes Professor of Plant Pathology Virginia Polytechnic Institute and State University Dr Eugene Smalley Emeritus Professor of Plant Pathology University of Wisconsin-Madison Dr Alden Townsend Research Geneticist USDA National Arboretum James Sherald Plant Pathologist National Park Service and Dr Richard Campana Emeritus Professor of Plant Pathology University of Maine Thanks for review of practical content are extended to Jim Hermann of Minneapolis Park and Recreation Board for review of the manuscript

Cover photo Branch flagging symptoms from a single point of Dutch elm disease infection in crown of elm (Photo courtesy of Dr R Jay Stipes)

The use of trade of firm names in this publication is for reader information and does not imply endorsement by the US Department of Agriculture of any product or service

Contents

bull Introduction bull Symptoms bull Distinguishing Dutch Elm Disease

from other problems bull Disease Cycle of Dutch Elm Disease bull Managing Dutch Elm Disease bull Trees in Natural Stands and Wild Areas bull Deciding Which Management Practices to Use bull Bibliography

Introduction

At one time the American elm was considered to be an ideal street tree because it was graceful long-lived fast growing and tolerant of compacted soils and air pollution Then Dutch elm disease (DED) was introduced and began devastating the elm population Estimates of DED losses of elm in communities and woodlands across the US are staggering (figure 1) Because elm is so well-suited to urban environments it continues to be a valued component of the urban forest despite the losses from DED The challenge before us is to reduce the loss of remaining elms and to choose suitable replacement trees for the ones we cannot save

This guide provides an update for urban foresters and tree care specialists with the latest information and management options available for Dutch elm disease

Figure 1 This photo is all too typical of the devastation caused by Dutch elm disease Once a tree in a row is infected the disease can move through connected root systems to kill the entire row (Photo courtesy of USDA Forest Service via Dr R Jay Stipes Virginia Polytechnic Institute and State University)

Symptoms

DED symptoms are the result of a fungus infecting the vascular (water conducting) system of the tree Infection by the fungus results in clogging of vascular tissues preventing water movement to the crown and causing visual symptoms as the tree wilts and dies

Foliage symptoms Symptoms of DED begin as wilting of leaves and proceed to yellowing and browning The pattern of symptom progression within the crown varies depending on where the fungus is introduced to the tree If the fungus enters the tree through roots grafted to infected trees (see disease cycle section) the symptoms may begin in the lower crown on the side nearest the graft and the entire crown may be affected very rapidly If infection begins in the upper crown symptoms often first appear at the end of an individual branch (called flagging) and progress downward in the crown (cover photo)

Multiple branches may be individually infected resulting in symptom development at several locations in the crown (figure 2) Symptoms begin in late spring or any time later during the growing season However if the tree was infected the previous year (and not detected) symptoms may first be observed in early spring Symptoms may progress throughout the whole tree in a single season or may take two or more years

Figure 2 Branch death or Flagging at multiple locations in the crown of a diseased elm (Photo courtesy of Dr Steve KatovichUSDA Forest Service St PaulMN)

Vascular symptoms Branches and stems of elms infected by the DED fungus typically develop dark streaks of discoloration To detect discoloration cut through and peel off the bark of a dying branch to expose the outer rings of wood In newly infected branches brown streaks characteristically appear in the sapwood of the current year (figure 3) It is important to cut deeply into the wood or look at the branch in cross section for two reasons (1) As the season progresses the staining may be overlaid by unstained wood and (2) if infection occurred in the previous year the current sapwood may not be discolored

Figure 3 Brown streaking develops in sapwood of branches infected by Dutch elm disease fungus Streaking is visible here (from left to right) in (1) the newly formed sapwood (2) spring sapwood overlaid by uninfected summer wood and (3) is absent in an uninfected branch (Photo courtesy of the America Phytopathological Society)

Distinguishing Dutch Elm Disease From Other Problems

Other pest problems commonly observed on elm include leaf spot diseases which cause dark spots of dead tissue in the leaves and elm leaf beetles which eat holes in the leaves These problems are easily distinguished from DED Elm leaf beetles do not carry the Dutch elm disease fungus as elm bark beetles do

Two other diseases elm yellows and bacterial leaf scorch are more easily confused with DED The symptoms of these diseases are compared to DED in table 1

Elm yellows This disease which is also called elm phloem necrosis is caused by a phytoplasma (microscopic bacteria-like organism) which systemically infects the phloem tissue (inner bark) of the tree It is a serious disease that causes tree death Symptoms of elm yellows differ from DED in that the leaves turn yellow (not brown and wilted) and drop prematurely and the symptoms appear in the entire crown at the same time The brown streaking which DED causes in the sapwood is absent but the inner bark develops a tan discoloration and a characteristic wintergreen odor

Bacterial leaf scorch This disease is caused by the bacterium Xylella fastidiosa which infects and clogs the water conducting tissues of the tree Infection by this bacterium causes a slow decline over many years Once a tree is infected symptoms recur annually Symptoms of scorch are irregular browning along the leaf margin with a yellow border between green and scorched leaf tissue Older leaves on a branch are affected first Disease Cycle of Dutch Elm Disease

The biology or disease cycle of DED depends upon the host the fungus and the means by which the fungus moves into new host trees (figure 4)

Figure 4 The disease cycle of Dutch elm disease is closely linked to the life cycle of elm bark beetles

(Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The elm host Native species of North American elms vary in their susceptibility to DED even within species American elm (Ulmus americana L) is generally highly susceptible Winged elm (U alata Michx) September elm (U serotina Sarg) slippery elm (U rubra Muhl) rock elm (U thomasii Sarg) and cedar elm (U crassifolia Nutt) range from susceptible to somewhat resistant No native elms are immune to DED but some individuals or cultivars have a higher tolerance (and thus may recover from or survive with infection) or resistance to DED Many European and Asiatic elms are less susceptible than American elm

In addition to genetic factors present in some cultivars and species physical factors affect tree susceptibility These factors include time of year climatic conditions (such as drought) and vitality of the tree Water conducting elements are most susceptible to infection as they are being produced in the spring thus elms are most susceptible to infection after earliest leafing out to midsummer Trees are less susceptible under drought conditions Vigorously growing trees are generally more susceptible than slower growing trees

The Dutch elm disease fungus DED can be caused by either of two closely related species of fungi Ophiostoma ulmi (Buism) Nannf (formerly called Ceratocystis ulmi) and Ophiostoma novo-ulmi Brasier The latter which is more aggressive in causing disease was recently recognized as being a separate species The DED fungus was first introduced to the US on diseased elm logs from Europe prior to 1930 It is unknown when the more aggressive species became established in the US however it was possibly present as early as the 1940s- 1950s and most likely caused much of the devastating mortality through the 1970s The less aggressive species is becoming increasingly rare in nature and the aggressive species is thought to be responsible for most of the current mortality Although some local resurgence of DED has been observed there is no evidence that it is due to a change in the pathogen Localized resurgence is more likely due to the following (1) a decrease in vigilance in monitoring and sanitation (2) a build-up in populations of the insect vectors or (3) ingrowth of susceptible host trees in the wild

Spread by elm bark beetles Overland spread of DED is closely linked to the life cycles of the native elm bark beetle (Hylurgopinus rufipes Eich) and the smaller European elm bark beetle (Scolytus multistriatus Marsh) (figure 5) Both beetles are attracted to stressed dying or dead elm wood to complete the breeding stage of their life cycle The adult beetles tunnel into the bark and lay their eggs in tunnels (called galleries) in the inner bark The eggs hatch and the larvae feed in the inner bark and sapwood

The larvae mature into adults and emerge from the elm wood If the DED fungus was present in the wood that the beetles infested the fungus produces sticky spores in the beetle galleries Spores of the DED fungus are eaten by or stick to the adult beetles as they emerge from diseased trees Adult beetles then visit healthy trees feed in twig crotches or branch inner bark and introduce the fungus into or near severed wood vessels as they feed

Figure 5 Overland spread of DED is closely tied to the life cycles of the Native elm bark beetle (top) and smaller European elm bark beetle (below) Note that the smaller European elm bark beetle is actually larger

than the native elm bark beetle (Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The importance of the two bark beetle species as vectors of DED varies across the range of elms In northern areas (northern parts of Minnesota Wisconsin Maine New York and New England and most of Canada where winter temperatures below -6deg F are common) the native elm bark beetle is the predominant vector In other parts of North America the smaller European elm bark beetle predominates The life habits of the adults of the two species differ considerably which has implications for management opportunities These differences are described below

Smaller European elm bark beetles overwinter as larvae or adults within the stem of the tree where they hatched They emerge as adults in spring to feed in twig crotches of healthy trees where they can introduce spores of the DED fungus to the crown High numbers of beetles frequently will feed in a single tree resulting in multiple points of infection The cycle is repeated when beetles then seek out diseased and dying wood to breed in throughout the growing season completing two or more generations per year They have the potential to rapidly build up high populations

Adult native elm bark beetles tunnel into the bark on the lower stems of healthy elms to overwinter In spring they emerge to feed in the inner bark of elm branches and small stems before beginning their breeding cycle They repeat their life cycle as previously described They can transmit the DED fungus to healthy trees during the construction of overwintering sites in fall or more commonly during feeding in spring

Once the DED fungus is introduced into the upper crown of healthy elms by bark beetles it slowly moves downward killing the

branch as it goes Disease progression may occur rapidly killing the tree by the end of the growing season or may progress gradually over a period of two or more years It is also possible that the tree may recover The success and rate of progression within the tree depends on tree size time and location of infection in the tree climatic conditions and response of the host tree Spread through grafted roots Roots of the same or closely related tree species growing near each other often cross each other in the soil and eventually fuse (become grafted) to each other

The DED fungus can move from infected trees to adjacent trees through these grafted roots Infections that occur through root grafts can spread very rapidly throughout the tree as the fungus is carried upward in the sapstream Root graft spread of DED is a very significant cause of tree death in urban areas where elms are closely spaced (figure 6)

Figure 6 Where elms are closely spaced the Dutch elm disease fungus may move down a row of trees through grafted roots Removing trees without breaking root grafts may not keep the fungus from moving into adjacent trees (Photo courtesy of Dr Joseph OBrien USDA Forest Service St Paul MN)

Managing Dutch Elm Disease

DED is managed by interrupting the disease cycle The most effective means of breaking the cycle is early and thorough sanitation to limit the population of the insects that transmit the fungus from tree to tree Other useful means of affecting the disease cycle include using insecticides to kill the insect vector breaking root grafts between trees injecting individual trees with fungicides to prevent or halt the fungus pruning out early infections and planting DED tolerant or resistant elm cultivars or other tree species

Sanitation to reduce insect vectors Many communities have been able to maintain a healthy population of mature elms through a vigilant program of identification and removal of diseased elms and systematic pruning of weakened dying or dead branches Sanitation by prompt removal of diseased trees or branches reduces breeding sites for elm bark beetles and eliminates the source of the DED fungus To be completely effective in interrupting the spread of the disease by elm bark beetles stems and branches of DED infected trees must be de-barked destroyed or utilized before the bark beetles emerge During the growing season removal should be completed within 2 to 3 weeks of detection During the dormant season removal should be completed before April when overwintering beetles may begin to emerge

Wood from infected trees can be destroyed by chipping burning or burying Wood may be retained for use as firewood or sawlogs if it is de-barked or covered from April 15th to October 15th with 4 to 6 mil plastic The edges of the cover must be buried or sealed to the ground If it is impossible to destroy all elm wood before the beetles emerge the wood can be sprayed with a registered insecticide until disposal is possible If insecticides are used consider potential exposure to chemical residues when burning or handling the treated wood Many communities have regulations on the removal of diseased elms and storage of elm firewood make sure your activities comply with local regulations

Insecticides to kill insect vectors In areas where the native elm bark beetle is the principal vector sanitation may be augmented by applying a registered insecticide to the lower stem of healthy elms in late summer to early fall (ie at the first sign of autumn leaf color change) to kill adult beetles as they prepare overwintering sites In areas where the smaller European elm bark beetle are common spring feeding in twig crotches can be prevented by spraying the crowns of elm trees with a registered insecticide However this may not be a preferred treatment method because of the difficulty in getting thorough coverage of all susceptible twig tissue the risk of insecticide drift and exposure and high expense

Insecticide registrations and recommendations are frequently updated and may vary considerably between states Cooperative Extension Services at land grant colleges and certified arborists are able to provide current insecticide recommendations

Disruption of root grafts Large trees within 25 to 50 feet of each other are likely to have root grafts Breaking root grafts between infected trees and adjacent healthy trees is an important means to prevent movement of the fungus into the healthy trees Root grafts should also be disrupted between the healthy tree adjacent to a diseased tree and the next healthy tree It may even be desirable to sever grafts between very valuable trees before DED is observed in the vicinity as a proactive measure

Root graft disruption should be completed before the infected trees are removed Otherwise the transpirational pull from healthy trees will rapidly draw in the contents of diseased trees root system when the vascular tension on the roots of the diseased tree is released by severing the stem Root graft disruption can be accomplished by use of a vibratory plow or any trenching machine equipped with the longest blade available (preferably five-feet long but at least three-feet long) Biocidal soil fumigants may also be used to kill root

grafts if no other alternatives are available However these chemicals are generally restricted use pesticides and may only be applied by professional pesticide applicators In addition biocidal chemicals may not be effective if soil temperatures are below 50 degF Injecting elms with fungicide Certain fungicides when properly injected are effective in protecting elm trees from infection via beetle transmission This treatment is expensive and must be repeated every one to three seasons thus it is appropriate only for high value or historically important trees The treatment itself also may pose risks to the health of the tree

Figure 7

Macroinjection of fungicide into the root flare of an elm tree (Photo courtesy of Mark Stennes certified arborist St Paul MN)

In order to be effective the fungicide must be present at adequate concentration at all potential points of infection Thus the dosage and means of application are critical to success The injection of chemical into root flares in large volumes of water (macroinjection) provides thorough distribution of chemical in the crown (figure 7) Microinjection (injection of small volumes of concentrated chemical) is also an option although its efficacy compared to macroinjection has not been thoroughly researched Preferably injections should be done soon after the earliest leaves have fully expanded but may be done from then to the end of the growing season Label rates of concentration for chemical application are updated to reflect the most recent findings on effectiveness always follow the current label

Harmful effects of fungicide injection have sometimes been reported and include occasional leaf scorching or loss Elms generally recover from this damage Also drilling injection holes results in wounding which if repeated annually may eventually result in significant discoloration and decay Following fungicide injection with a flush of clean water can reduce damage to the cambium Some chemicals are able to protect trees for up to three seasons thus minimizing the frequency of treatments

Several fungicides are registered for injection to prevent DED infection These chemicals vary in duration of protective effects means of application risk of damage to the tree documentation of effectiveness and cost Certified arborists or Cooperative Extension Services at land grant colleges are able to provide current recommendations on product availability and effectiveness Eradicating Dutch elm disease from newly infected trees If a new crown infection of DED is detected early enough there is opportunity to save a tree through pruning fungicide injection or both Eradicative treatment is not possible on trees that have become infected via root graft transmission Pruning which can literally eradicate the fungus from the tree by removing it has a high probability of saving a newly infected tree that has less than 5 of its crown affected To be a candidate for eradicative pruning the infection must be a new infection (not a residual infection from the previous season) and be present only in the upper crown (not yet present in the main stem) Since infection may be more advanced than symptoms indicate it is important to peel off the bark of infected branches and locate the staining which indicates the presence of the fungus All infected branches should be removed at a branch fork at least 5 feet and preferably 10 feet below the last sign of streaking in the sapwood (figure 8) Whenever elm branches are pruned during the growing season pruning paint specifically formulated for use on trees should be applied to prevent attraction of elm bark beetles to the wounded trees (Painting tree wounds is generally not recommended except to prevent disease transmission in oaks and elms)

Figure 8 Eradicative pruning of branches infected with DED may be effective if there is adequate length (5 to 10 feet) of clearwood between the infected tissue and the remainder of the crown or if the tree has been properly treated with fungicide (Artwork courtesy of Jim Lockyer USDA Forest Service Radnor PA)

Pruning is more likely to be effective if augmented by systemic injection of fungicides Proper use of fungicides eliminates the need to eradicate all infected tissues from the tree although all dead branches should eventually be removed Whereas pruning alone is not effective against residual infections fungicide injection may be If fungicides are used they should be injected prior to removal of diseased branches The keys to successful eradicative treatment are early detection and prompt treatment

Planting Dutch Elm Disease resistant or tolerant trees Planting trees with resistance or tolerance to DED is a valid management option However selecting only a few cultivars limits the genetic variability of the population This could lead to increased risk of widespread losses if these cultivars are found to be susceptible to tree health problems such as poor adaptation to site air pollution other elm pests or pathogens (such as elm yellows or elm leaf beetle) or even other strains of DED which may eventually develop Thus it is prudent to plant a mixture of suitable cultivars of as many elm genotypes as possible Santamour and Bentz (1995) recently published a checklist and brief description of elm cultivars in North America The only true American elms on that list that are commercially available and have strong evidence of DED tolerance or resistance are the Princeton Elm the American Liberty multi-clone and Independence which is one of the cultivars in the American Liberty multi-clone Two additional American elms Valley Forge and New Harmony were released by the USDA National Arboretum since the Santamour and Bentz listing was prepared These two cultivars which exhibit high tolerance to DED should be available through retail nurseries by 2001

Besides true American elms there are many other hybrid elm crosses and species of elm that have high tolerance or resistance to DED Several of these have attractive form are well suited to urban environments and are readily available (figure 9) Many of these are listed and described by Santamour and Bentz (1995) in the previously mentioned checklist

Figure 9 Cultivars of elm selected for resistance to DED are available This selection of Ulmus japonica demonstrates the potential these elms have as landscape trees (Photo courtesy of Dr Eugene Smalley University of Wisconsin--Madison)

In addition to careful selection of the tree species and cultivar location and spacing are also important to reduce losses from DED When selecting landscape trees and their locations plant a mixture of tree species appropriate to the site In addition to the species diversity consider spacing of the trees Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity

Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and DED fungus to infect high value landscape trees Management is necessary in order to protect urban elms

The most effective management option to reduce both the bark beetle vectors and the DED fungus is sanitation to promptly remove stressed dead and dying elms as previously described However this intensity of treatment is often not feasible

A trap tree method was developed in the 1980s to more cost effectively reduce populations of elm bark beetles Under this method DED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark The bark beetles are attracted to the dying trees but the rapidly drying bark is unsuitable for them to complete their lifecycle and the bark beetle populations are reduced However treated trees may then become hazard trees with high risk of falling and causing personal injury or property damage

Another option in wild areas or natural stands other than accepting losses from DED is to eliminate all elms and manage for alternative species However it is often desirable to retain elms for biodiversity aesthetic economic or other reasons

Deciding Which Management Practices to Use Different management strategies will be applicable depending on whether you are working with a community program or trying to protect individual trees In a community program the objective will be to protect a population of elms Individual landowners however may have no control over what neighbors do with their elms but may want to protect or save their own trees The amount of money an individual or community is able to spend will also vary

Where you have no control over the management of surrounding trees the only options available are treatments to protect or save individual trees Good sanitation practices and disruption of root grafts are necessary on individual properties but these practices alone will not protect a tree from disease transmission by bark beetles from other properties Preventive fungicide injection eradicative pruning and fungicide injection and insecticide treatment are generally the only options available for individual trees

In a community program resources to spend on individual trees may be low but there is more opportunity to manage populations of elms Where there are continuous elms root graft disruption is essential to halt the spread Sanitation is key to reducing beetle and DED populations and is effective Community ordinances can be established to encourage prompt removal of diseased trees and

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Introduction

At one time the American elm was considered to be an ideal street tree because it was graceful long-lived fast growing and tolerant of compacted soils and air pollution Then Dutch elm disease (DED) was introduced and began devastating the elm population Estimates of DED losses of elm in communities and woodlands across the US are staggering (figure 1) Because elm is so well-suited to urban environments it continues to be a valued component of the urban forest despite the losses from DED The challenge before us is to reduce the loss of remaining elms and to choose suitable replacement trees for the ones we cannot save

This guide provides an update for urban foresters and tree care specialists with the latest information and management options available for Dutch elm disease

Figure 1 This photo is all too typical of the devastation caused by Dutch elm disease Once a tree in a row is infected the disease can move through connected root systems to kill the entire row (Photo courtesy of USDA Forest Service via Dr R Jay Stipes Virginia Polytechnic Institute and State University)

Symptoms

DED symptoms are the result of a fungus infecting the vascular (water conducting) system of the tree Infection by the fungus results in clogging of vascular tissues preventing water movement to the crown and causing visual symptoms as the tree wilts and dies

Foliage symptoms Symptoms of DED begin as wilting of leaves and proceed to yellowing and browning The pattern of symptom progression within the crown varies depending on where the fungus is introduced to the tree If the fungus enters the tree through roots grafted to infected trees (see disease cycle section) the symptoms may begin in the lower crown on the side nearest the graft and the entire crown may be affected very rapidly If infection begins in the upper crown symptoms often first appear at the end of an individual branch (called flagging) and progress downward in the crown (cover photo)

Multiple branches may be individually infected resulting in symptom development at several locations in the crown (figure 2) Symptoms begin in late spring or any time later during the growing season However if the tree was infected the previous year (and not detected) symptoms may first be observed in early spring Symptoms may progress throughout the whole tree in a single season or may take two or more years

Figure 2 Branch death or Flagging at multiple locations in the crown of a diseased elm (Photo courtesy of Dr Steve KatovichUSDA Forest Service St PaulMN)

Vascular symptoms Branches and stems of elms infected by the DED fungus typically develop dark streaks of discoloration To detect discoloration cut through and peel off the bark of a dying branch to expose the outer rings of wood In newly infected branches brown streaks characteristically appear in the sapwood of the current year (figure 3) It is important to cut deeply into the wood or look at the branch in cross section for two reasons (1) As the season progresses the staining may be overlaid by unstained wood and (2) if infection occurred in the previous year the current sapwood may not be discolored

Figure 3 Brown streaking develops in sapwood of branches infected by Dutch elm disease fungus Streaking is visible here (from left to right) in (1) the newly formed sapwood (2) spring sapwood overlaid by uninfected summer wood and (3) is absent in an uninfected branch (Photo courtesy of the America Phytopathological Society)

Distinguishing Dutch Elm Disease From Other Problems

Other pest problems commonly observed on elm include leaf spot diseases which cause dark spots of dead tissue in the leaves and elm leaf beetles which eat holes in the leaves These problems are easily distinguished from DED Elm leaf beetles do not carry the Dutch elm disease fungus as elm bark beetles do

Two other diseases elm yellows and bacterial leaf scorch are more easily confused with DED The symptoms of these diseases are compared to DED in table 1

Elm yellows This disease which is also called elm phloem necrosis is caused by a phytoplasma (microscopic bacteria-like organism) which systemically infects the phloem tissue (inner bark) of the tree It is a serious disease that causes tree death Symptoms of elm yellows differ from DED in that the leaves turn yellow (not brown and wilted) and drop prematurely and the symptoms appear in the entire crown at the same time The brown streaking which DED causes in the sapwood is absent but the inner bark develops a tan discoloration and a characteristic wintergreen odor

Bacterial leaf scorch This disease is caused by the bacterium Xylella fastidiosa which infects and clogs the water conducting tissues of the tree Infection by this bacterium causes a slow decline over many years Once a tree is infected symptoms recur annually Symptoms of scorch are irregular browning along the leaf margin with a yellow border between green and scorched leaf tissue Older leaves on a branch are affected first Disease Cycle of Dutch Elm Disease

The biology or disease cycle of DED depends upon the host the fungus and the means by which the fungus moves into new host trees (figure 4)

Figure 4 The disease cycle of Dutch elm disease is closely linked to the life cycle of elm bark beetles

(Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The elm host Native species of North American elms vary in their susceptibility to DED even within species American elm (Ulmus americana L) is generally highly susceptible Winged elm (U alata Michx) September elm (U serotina Sarg) slippery elm (U rubra Muhl) rock elm (U thomasii Sarg) and cedar elm (U crassifolia Nutt) range from susceptible to somewhat resistant No native elms are immune to DED but some individuals or cultivars have a higher tolerance (and thus may recover from or survive with infection) or resistance to DED Many European and Asiatic elms are less susceptible than American elm

In addition to genetic factors present in some cultivars and species physical factors affect tree susceptibility These factors include time of year climatic conditions (such as drought) and vitality of the tree Water conducting elements are most susceptible to infection as they are being produced in the spring thus elms are most susceptible to infection after earliest leafing out to midsummer Trees are less susceptible under drought conditions Vigorously growing trees are generally more susceptible than slower growing trees

The Dutch elm disease fungus DED can be caused by either of two closely related species of fungi Ophiostoma ulmi (Buism) Nannf (formerly called Ceratocystis ulmi) and Ophiostoma novo-ulmi Brasier The latter which is more aggressive in causing disease was recently recognized as being a separate species The DED fungus was first introduced to the US on diseased elm logs from Europe prior to 1930 It is unknown when the more aggressive species became established in the US however it was possibly present as early as the 1940s- 1950s and most likely caused much of the devastating mortality through the 1970s The less aggressive species is becoming increasingly rare in nature and the aggressive species is thought to be responsible for most of the current mortality Although some local resurgence of DED has been observed there is no evidence that it is due to a change in the pathogen Localized resurgence is more likely due to the following (1) a decrease in vigilance in monitoring and sanitation (2) a build-up in populations of the insect vectors or (3) ingrowth of susceptible host trees in the wild

Spread by elm bark beetles Overland spread of DED is closely linked to the life cycles of the native elm bark beetle (Hylurgopinus rufipes Eich) and the smaller European elm bark beetle (Scolytus multistriatus Marsh) (figure 5) Both beetles are attracted to stressed dying or dead elm wood to complete the breeding stage of their life cycle The adult beetles tunnel into the bark and lay their eggs in tunnels (called galleries) in the inner bark The eggs hatch and the larvae feed in the inner bark and sapwood

The larvae mature into adults and emerge from the elm wood If the DED fungus was present in the wood that the beetles infested the fungus produces sticky spores in the beetle galleries Spores of the DED fungus are eaten by or stick to the adult beetles as they emerge from diseased trees Adult beetles then visit healthy trees feed in twig crotches or branch inner bark and introduce the fungus into or near severed wood vessels as they feed

Figure 5 Overland spread of DED is closely tied to the life cycles of the Native elm bark beetle (top) and smaller European elm bark beetle (below) Note that the smaller European elm bark beetle is actually larger

than the native elm bark beetle (Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The importance of the two bark beetle species as vectors of DED varies across the range of elms In northern areas (northern parts of Minnesota Wisconsin Maine New York and New England and most of Canada where winter temperatures below -6deg F are common) the native elm bark beetle is the predominant vector In other parts of North America the smaller European elm bark beetle predominates The life habits of the adults of the two species differ considerably which has implications for management opportunities These differences are described below

Smaller European elm bark beetles overwinter as larvae or adults within the stem of the tree where they hatched They emerge as adults in spring to feed in twig crotches of healthy trees where they can introduce spores of the DED fungus to the crown High numbers of beetles frequently will feed in a single tree resulting in multiple points of infection The cycle is repeated when beetles then seek out diseased and dying wood to breed in throughout the growing season completing two or more generations per year They have the potential to rapidly build up high populations

Adult native elm bark beetles tunnel into the bark on the lower stems of healthy elms to overwinter In spring they emerge to feed in the inner bark of elm branches and small stems before beginning their breeding cycle They repeat their life cycle as previously described They can transmit the DED fungus to healthy trees during the construction of overwintering sites in fall or more commonly during feeding in spring

Once the DED fungus is introduced into the upper crown of healthy elms by bark beetles it slowly moves downward killing the

branch as it goes Disease progression may occur rapidly killing the tree by the end of the growing season or may progress gradually over a period of two or more years It is also possible that the tree may recover The success and rate of progression within the tree depends on tree size time and location of infection in the tree climatic conditions and response of the host tree Spread through grafted roots Roots of the same or closely related tree species growing near each other often cross each other in the soil and eventually fuse (become grafted) to each other

The DED fungus can move from infected trees to adjacent trees through these grafted roots Infections that occur through root grafts can spread very rapidly throughout the tree as the fungus is carried upward in the sapstream Root graft spread of DED is a very significant cause of tree death in urban areas where elms are closely spaced (figure 6)

Figure 6 Where elms are closely spaced the Dutch elm disease fungus may move down a row of trees through grafted roots Removing trees without breaking root grafts may not keep the fungus from moving into adjacent trees (Photo courtesy of Dr Joseph OBrien USDA Forest Service St Paul MN)

Managing Dutch Elm Disease

DED is managed by interrupting the disease cycle The most effective means of breaking the cycle is early and thorough sanitation to limit the population of the insects that transmit the fungus from tree to tree Other useful means of affecting the disease cycle include using insecticides to kill the insect vector breaking root grafts between trees injecting individual trees with fungicides to prevent or halt the fungus pruning out early infections and planting DED tolerant or resistant elm cultivars or other tree species

Sanitation to reduce insect vectors Many communities have been able to maintain a healthy population of mature elms through a vigilant program of identification and removal of diseased elms and systematic pruning of weakened dying or dead branches Sanitation by prompt removal of diseased trees or branches reduces breeding sites for elm bark beetles and eliminates the source of the DED fungus To be completely effective in interrupting the spread of the disease by elm bark beetles stems and branches of DED infected trees must be de-barked destroyed or utilized before the bark beetles emerge During the growing season removal should be completed within 2 to 3 weeks of detection During the dormant season removal should be completed before April when overwintering beetles may begin to emerge

Wood from infected trees can be destroyed by chipping burning or burying Wood may be retained for use as firewood or sawlogs if it is de-barked or covered from April 15th to October 15th with 4 to 6 mil plastic The edges of the cover must be buried or sealed to the ground If it is impossible to destroy all elm wood before the beetles emerge the wood can be sprayed with a registered insecticide until disposal is possible If insecticides are used consider potential exposure to chemical residues when burning or handling the treated wood Many communities have regulations on the removal of diseased elms and storage of elm firewood make sure your activities comply with local regulations

Insecticides to kill insect vectors In areas where the native elm bark beetle is the principal vector sanitation may be augmented by applying a registered insecticide to the lower stem of healthy elms in late summer to early fall (ie at the first sign of autumn leaf color change) to kill adult beetles as they prepare overwintering sites In areas where the smaller European elm bark beetle are common spring feeding in twig crotches can be prevented by spraying the crowns of elm trees with a registered insecticide However this may not be a preferred treatment method because of the difficulty in getting thorough coverage of all susceptible twig tissue the risk of insecticide drift and exposure and high expense

Insecticide registrations and recommendations are frequently updated and may vary considerably between states Cooperative Extension Services at land grant colleges and certified arborists are able to provide current insecticide recommendations

Disruption of root grafts Large trees within 25 to 50 feet of each other are likely to have root grafts Breaking root grafts between infected trees and adjacent healthy trees is an important means to prevent movement of the fungus into the healthy trees Root grafts should also be disrupted between the healthy tree adjacent to a diseased tree and the next healthy tree It may even be desirable to sever grafts between very valuable trees before DED is observed in the vicinity as a proactive measure

Root graft disruption should be completed before the infected trees are removed Otherwise the transpirational pull from healthy trees will rapidly draw in the contents of diseased trees root system when the vascular tension on the roots of the diseased tree is released by severing the stem Root graft disruption can be accomplished by use of a vibratory plow or any trenching machine equipped with the longest blade available (preferably five-feet long but at least three-feet long) Biocidal soil fumigants may also be used to kill root

grafts if no other alternatives are available However these chemicals are generally restricted use pesticides and may only be applied by professional pesticide applicators In addition biocidal chemicals may not be effective if soil temperatures are below 50 degF Injecting elms with fungicide Certain fungicides when properly injected are effective in protecting elm trees from infection via beetle transmission This treatment is expensive and must be repeated every one to three seasons thus it is appropriate only for high value or historically important trees The treatment itself also may pose risks to the health of the tree

Figure 7

Macroinjection of fungicide into the root flare of an elm tree (Photo courtesy of Mark Stennes certified arborist St Paul MN)

In order to be effective the fungicide must be present at adequate concentration at all potential points of infection Thus the dosage and means of application are critical to success The injection of chemical into root flares in large volumes of water (macroinjection) provides thorough distribution of chemical in the crown (figure 7) Microinjection (injection of small volumes of concentrated chemical) is also an option although its efficacy compared to macroinjection has not been thoroughly researched Preferably injections should be done soon after the earliest leaves have fully expanded but may be done from then to the end of the growing season Label rates of concentration for chemical application are updated to reflect the most recent findings on effectiveness always follow the current label

Harmful effects of fungicide injection have sometimes been reported and include occasional leaf scorching or loss Elms generally recover from this damage Also drilling injection holes results in wounding which if repeated annually may eventually result in significant discoloration and decay Following fungicide injection with a flush of clean water can reduce damage to the cambium Some chemicals are able to protect trees for up to three seasons thus minimizing the frequency of treatments

Several fungicides are registered for injection to prevent DED infection These chemicals vary in duration of protective effects means of application risk of damage to the tree documentation of effectiveness and cost Certified arborists or Cooperative Extension Services at land grant colleges are able to provide current recommendations on product availability and effectiveness Eradicating Dutch elm disease from newly infected trees If a new crown infection of DED is detected early enough there is opportunity to save a tree through pruning fungicide injection or both Eradicative treatment is not possible on trees that have become infected via root graft transmission Pruning which can literally eradicate the fungus from the tree by removing it has a high probability of saving a newly infected tree that has less than 5 of its crown affected To be a candidate for eradicative pruning the infection must be a new infection (not a residual infection from the previous season) and be present only in the upper crown (not yet present in the main stem) Since infection may be more advanced than symptoms indicate it is important to peel off the bark of infected branches and locate the staining which indicates the presence of the fungus All infected branches should be removed at a branch fork at least 5 feet and preferably 10 feet below the last sign of streaking in the sapwood (figure 8) Whenever elm branches are pruned during the growing season pruning paint specifically formulated for use on trees should be applied to prevent attraction of elm bark beetles to the wounded trees (Painting tree wounds is generally not recommended except to prevent disease transmission in oaks and elms)

Figure 8 Eradicative pruning of branches infected with DED may be effective if there is adequate length (5 to 10 feet) of clearwood between the infected tissue and the remainder of the crown or if the tree has been properly treated with fungicide (Artwork courtesy of Jim Lockyer USDA Forest Service Radnor PA)

Pruning is more likely to be effective if augmented by systemic injection of fungicides Proper use of fungicides eliminates the need to eradicate all infected tissues from the tree although all dead branches should eventually be removed Whereas pruning alone is not effective against residual infections fungicide injection may be If fungicides are used they should be injected prior to removal of diseased branches The keys to successful eradicative treatment are early detection and prompt treatment

Planting Dutch Elm Disease resistant or tolerant trees Planting trees with resistance or tolerance to DED is a valid management option However selecting only a few cultivars limits the genetic variability of the population This could lead to increased risk of widespread losses if these cultivars are found to be susceptible to tree health problems such as poor adaptation to site air pollution other elm pests or pathogens (such as elm yellows or elm leaf beetle) or even other strains of DED which may eventually develop Thus it is prudent to plant a mixture of suitable cultivars of as many elm genotypes as possible Santamour and Bentz (1995) recently published a checklist and brief description of elm cultivars in North America The only true American elms on that list that are commercially available and have strong evidence of DED tolerance or resistance are the Princeton Elm the American Liberty multi-clone and Independence which is one of the cultivars in the American Liberty multi-clone Two additional American elms Valley Forge and New Harmony were released by the USDA National Arboretum since the Santamour and Bentz listing was prepared These two cultivars which exhibit high tolerance to DED should be available through retail nurseries by 2001

Besides true American elms there are many other hybrid elm crosses and species of elm that have high tolerance or resistance to DED Several of these have attractive form are well suited to urban environments and are readily available (figure 9) Many of these are listed and described by Santamour and Bentz (1995) in the previously mentioned checklist

Figure 9 Cultivars of elm selected for resistance to DED are available This selection of Ulmus japonica demonstrates the potential these elms have as landscape trees (Photo courtesy of Dr Eugene Smalley University of Wisconsin--Madison)

In addition to careful selection of the tree species and cultivar location and spacing are also important to reduce losses from DED When selecting landscape trees and their locations plant a mixture of tree species appropriate to the site In addition to the species diversity consider spacing of the trees Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity

Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and DED fungus to infect high value landscape trees Management is necessary in order to protect urban elms

The most effective management option to reduce both the bark beetle vectors and the DED fungus is sanitation to promptly remove stressed dead and dying elms as previously described However this intensity of treatment is often not feasible

A trap tree method was developed in the 1980s to more cost effectively reduce populations of elm bark beetles Under this method DED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark The bark beetles are attracted to the dying trees but the rapidly drying bark is unsuitable for them to complete their lifecycle and the bark beetle populations are reduced However treated trees may then become hazard trees with high risk of falling and causing personal injury or property damage

Another option in wild areas or natural stands other than accepting losses from DED is to eliminate all elms and manage for alternative species However it is often desirable to retain elms for biodiversity aesthetic economic or other reasons

Deciding Which Management Practices to Use Different management strategies will be applicable depending on whether you are working with a community program or trying to protect individual trees In a community program the objective will be to protect a population of elms Individual landowners however may have no control over what neighbors do with their elms but may want to protect or save their own trees The amount of money an individual or community is able to spend will also vary

Where you have no control over the management of surrounding trees the only options available are treatments to protect or save individual trees Good sanitation practices and disruption of root grafts are necessary on individual properties but these practices alone will not protect a tree from disease transmission by bark beetles from other properties Preventive fungicide injection eradicative pruning and fungicide injection and insecticide treatment are generally the only options available for individual trees

In a community program resources to spend on individual trees may be low but there is more opportunity to manage populations of elms Where there are continuous elms root graft disruption is essential to halt the spread Sanitation is key to reducing beetle and DED populations and is effective Community ordinances can be established to encourage prompt removal of diseased trees and

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Vascular symptoms Branches and stems of elms infected by the DED fungus typically develop dark streaks of discoloration To detect discoloration cut through and peel off the bark of a dying branch to expose the outer rings of wood In newly infected branches brown streaks characteristically appear in the sapwood of the current year (figure 3) It is important to cut deeply into the wood or look at the branch in cross section for two reasons (1) As the season progresses the staining may be overlaid by unstained wood and (2) if infection occurred in the previous year the current sapwood may not be discolored

Figure 3 Brown streaking develops in sapwood of branches infected by Dutch elm disease fungus Streaking is visible here (from left to right) in (1) the newly formed sapwood (2) spring sapwood overlaid by uninfected summer wood and (3) is absent in an uninfected branch (Photo courtesy of the America Phytopathological Society)

Distinguishing Dutch Elm Disease From Other Problems

Other pest problems commonly observed on elm include leaf spot diseases which cause dark spots of dead tissue in the leaves and elm leaf beetles which eat holes in the leaves These problems are easily distinguished from DED Elm leaf beetles do not carry the Dutch elm disease fungus as elm bark beetles do

Two other diseases elm yellows and bacterial leaf scorch are more easily confused with DED The symptoms of these diseases are compared to DED in table 1

Elm yellows This disease which is also called elm phloem necrosis is caused by a phytoplasma (microscopic bacteria-like organism) which systemically infects the phloem tissue (inner bark) of the tree It is a serious disease that causes tree death Symptoms of elm yellows differ from DED in that the leaves turn yellow (not brown and wilted) and drop prematurely and the symptoms appear in the entire crown at the same time The brown streaking which DED causes in the sapwood is absent but the inner bark develops a tan discoloration and a characteristic wintergreen odor

Bacterial leaf scorch This disease is caused by the bacterium Xylella fastidiosa which infects and clogs the water conducting tissues of the tree Infection by this bacterium causes a slow decline over many years Once a tree is infected symptoms recur annually Symptoms of scorch are irregular browning along the leaf margin with a yellow border between green and scorched leaf tissue Older leaves on a branch are affected first Disease Cycle of Dutch Elm Disease

The biology or disease cycle of DED depends upon the host the fungus and the means by which the fungus moves into new host trees (figure 4)

Figure 4 The disease cycle of Dutch elm disease is closely linked to the life cycle of elm bark beetles

(Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The elm host Native species of North American elms vary in their susceptibility to DED even within species American elm (Ulmus americana L) is generally highly susceptible Winged elm (U alata Michx) September elm (U serotina Sarg) slippery elm (U rubra Muhl) rock elm (U thomasii Sarg) and cedar elm (U crassifolia Nutt) range from susceptible to somewhat resistant No native elms are immune to DED but some individuals or cultivars have a higher tolerance (and thus may recover from or survive with infection) or resistance to DED Many European and Asiatic elms are less susceptible than American elm

In addition to genetic factors present in some cultivars and species physical factors affect tree susceptibility These factors include time of year climatic conditions (such as drought) and vitality of the tree Water conducting elements are most susceptible to infection as they are being produced in the spring thus elms are most susceptible to infection after earliest leafing out to midsummer Trees are less susceptible under drought conditions Vigorously growing trees are generally more susceptible than slower growing trees

The Dutch elm disease fungus DED can be caused by either of two closely related species of fungi Ophiostoma ulmi (Buism) Nannf (formerly called Ceratocystis ulmi) and Ophiostoma novo-ulmi Brasier The latter which is more aggressive in causing disease was recently recognized as being a separate species The DED fungus was first introduced to the US on diseased elm logs from Europe prior to 1930 It is unknown when the more aggressive species became established in the US however it was possibly present as early as the 1940s- 1950s and most likely caused much of the devastating mortality through the 1970s The less aggressive species is becoming increasingly rare in nature and the aggressive species is thought to be responsible for most of the current mortality Although some local resurgence of DED has been observed there is no evidence that it is due to a change in the pathogen Localized resurgence is more likely due to the following (1) a decrease in vigilance in monitoring and sanitation (2) a build-up in populations of the insect vectors or (3) ingrowth of susceptible host trees in the wild

Spread by elm bark beetles Overland spread of DED is closely linked to the life cycles of the native elm bark beetle (Hylurgopinus rufipes Eich) and the smaller European elm bark beetle (Scolytus multistriatus Marsh) (figure 5) Both beetles are attracted to stressed dying or dead elm wood to complete the breeding stage of their life cycle The adult beetles tunnel into the bark and lay their eggs in tunnels (called galleries) in the inner bark The eggs hatch and the larvae feed in the inner bark and sapwood

The larvae mature into adults and emerge from the elm wood If the DED fungus was present in the wood that the beetles infested the fungus produces sticky spores in the beetle galleries Spores of the DED fungus are eaten by or stick to the adult beetles as they emerge from diseased trees Adult beetles then visit healthy trees feed in twig crotches or branch inner bark and introduce the fungus into or near severed wood vessels as they feed

Figure 5 Overland spread of DED is closely tied to the life cycles of the Native elm bark beetle (top) and smaller European elm bark beetle (below) Note that the smaller European elm bark beetle is actually larger

than the native elm bark beetle (Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The importance of the two bark beetle species as vectors of DED varies across the range of elms In northern areas (northern parts of Minnesota Wisconsin Maine New York and New England and most of Canada where winter temperatures below -6deg F are common) the native elm bark beetle is the predominant vector In other parts of North America the smaller European elm bark beetle predominates The life habits of the adults of the two species differ considerably which has implications for management opportunities These differences are described below

Smaller European elm bark beetles overwinter as larvae or adults within the stem of the tree where they hatched They emerge as adults in spring to feed in twig crotches of healthy trees where they can introduce spores of the DED fungus to the crown High numbers of beetles frequently will feed in a single tree resulting in multiple points of infection The cycle is repeated when beetles then seek out diseased and dying wood to breed in throughout the growing season completing two or more generations per year They have the potential to rapidly build up high populations

Adult native elm bark beetles tunnel into the bark on the lower stems of healthy elms to overwinter In spring they emerge to feed in the inner bark of elm branches and small stems before beginning their breeding cycle They repeat their life cycle as previously described They can transmit the DED fungus to healthy trees during the construction of overwintering sites in fall or more commonly during feeding in spring

Once the DED fungus is introduced into the upper crown of healthy elms by bark beetles it slowly moves downward killing the

branch as it goes Disease progression may occur rapidly killing the tree by the end of the growing season or may progress gradually over a period of two or more years It is also possible that the tree may recover The success and rate of progression within the tree depends on tree size time and location of infection in the tree climatic conditions and response of the host tree Spread through grafted roots Roots of the same or closely related tree species growing near each other often cross each other in the soil and eventually fuse (become grafted) to each other

The DED fungus can move from infected trees to adjacent trees through these grafted roots Infections that occur through root grafts can spread very rapidly throughout the tree as the fungus is carried upward in the sapstream Root graft spread of DED is a very significant cause of tree death in urban areas where elms are closely spaced (figure 6)

Figure 6 Where elms are closely spaced the Dutch elm disease fungus may move down a row of trees through grafted roots Removing trees without breaking root grafts may not keep the fungus from moving into adjacent trees (Photo courtesy of Dr Joseph OBrien USDA Forest Service St Paul MN)

Managing Dutch Elm Disease

DED is managed by interrupting the disease cycle The most effective means of breaking the cycle is early and thorough sanitation to limit the population of the insects that transmit the fungus from tree to tree Other useful means of affecting the disease cycle include using insecticides to kill the insect vector breaking root grafts between trees injecting individual trees with fungicides to prevent or halt the fungus pruning out early infections and planting DED tolerant or resistant elm cultivars or other tree species

Sanitation to reduce insect vectors Many communities have been able to maintain a healthy population of mature elms through a vigilant program of identification and removal of diseased elms and systematic pruning of weakened dying or dead branches Sanitation by prompt removal of diseased trees or branches reduces breeding sites for elm bark beetles and eliminates the source of the DED fungus To be completely effective in interrupting the spread of the disease by elm bark beetles stems and branches of DED infected trees must be de-barked destroyed or utilized before the bark beetles emerge During the growing season removal should be completed within 2 to 3 weeks of detection During the dormant season removal should be completed before April when overwintering beetles may begin to emerge

Wood from infected trees can be destroyed by chipping burning or burying Wood may be retained for use as firewood or sawlogs if it is de-barked or covered from April 15th to October 15th with 4 to 6 mil plastic The edges of the cover must be buried or sealed to the ground If it is impossible to destroy all elm wood before the beetles emerge the wood can be sprayed with a registered insecticide until disposal is possible If insecticides are used consider potential exposure to chemical residues when burning or handling the treated wood Many communities have regulations on the removal of diseased elms and storage of elm firewood make sure your activities comply with local regulations

Insecticides to kill insect vectors In areas where the native elm bark beetle is the principal vector sanitation may be augmented by applying a registered insecticide to the lower stem of healthy elms in late summer to early fall (ie at the first sign of autumn leaf color change) to kill adult beetles as they prepare overwintering sites In areas where the smaller European elm bark beetle are common spring feeding in twig crotches can be prevented by spraying the crowns of elm trees with a registered insecticide However this may not be a preferred treatment method because of the difficulty in getting thorough coverage of all susceptible twig tissue the risk of insecticide drift and exposure and high expense

Insecticide registrations and recommendations are frequently updated and may vary considerably between states Cooperative Extension Services at land grant colleges and certified arborists are able to provide current insecticide recommendations

Disruption of root grafts Large trees within 25 to 50 feet of each other are likely to have root grafts Breaking root grafts between infected trees and adjacent healthy trees is an important means to prevent movement of the fungus into the healthy trees Root grafts should also be disrupted between the healthy tree adjacent to a diseased tree and the next healthy tree It may even be desirable to sever grafts between very valuable trees before DED is observed in the vicinity as a proactive measure

Root graft disruption should be completed before the infected trees are removed Otherwise the transpirational pull from healthy trees will rapidly draw in the contents of diseased trees root system when the vascular tension on the roots of the diseased tree is released by severing the stem Root graft disruption can be accomplished by use of a vibratory plow or any trenching machine equipped with the longest blade available (preferably five-feet long but at least three-feet long) Biocidal soil fumigants may also be used to kill root

grafts if no other alternatives are available However these chemicals are generally restricted use pesticides and may only be applied by professional pesticide applicators In addition biocidal chemicals may not be effective if soil temperatures are below 50 degF Injecting elms with fungicide Certain fungicides when properly injected are effective in protecting elm trees from infection via beetle transmission This treatment is expensive and must be repeated every one to three seasons thus it is appropriate only for high value or historically important trees The treatment itself also may pose risks to the health of the tree

Figure 7

Macroinjection of fungicide into the root flare of an elm tree (Photo courtesy of Mark Stennes certified arborist St Paul MN)

In order to be effective the fungicide must be present at adequate concentration at all potential points of infection Thus the dosage and means of application are critical to success The injection of chemical into root flares in large volumes of water (macroinjection) provides thorough distribution of chemical in the crown (figure 7) Microinjection (injection of small volumes of concentrated chemical) is also an option although its efficacy compared to macroinjection has not been thoroughly researched Preferably injections should be done soon after the earliest leaves have fully expanded but may be done from then to the end of the growing season Label rates of concentration for chemical application are updated to reflect the most recent findings on effectiveness always follow the current label

Harmful effects of fungicide injection have sometimes been reported and include occasional leaf scorching or loss Elms generally recover from this damage Also drilling injection holes results in wounding which if repeated annually may eventually result in significant discoloration and decay Following fungicide injection with a flush of clean water can reduce damage to the cambium Some chemicals are able to protect trees for up to three seasons thus minimizing the frequency of treatments

Several fungicides are registered for injection to prevent DED infection These chemicals vary in duration of protective effects means of application risk of damage to the tree documentation of effectiveness and cost Certified arborists or Cooperative Extension Services at land grant colleges are able to provide current recommendations on product availability and effectiveness Eradicating Dutch elm disease from newly infected trees If a new crown infection of DED is detected early enough there is opportunity to save a tree through pruning fungicide injection or both Eradicative treatment is not possible on trees that have become infected via root graft transmission Pruning which can literally eradicate the fungus from the tree by removing it has a high probability of saving a newly infected tree that has less than 5 of its crown affected To be a candidate for eradicative pruning the infection must be a new infection (not a residual infection from the previous season) and be present only in the upper crown (not yet present in the main stem) Since infection may be more advanced than symptoms indicate it is important to peel off the bark of infected branches and locate the staining which indicates the presence of the fungus All infected branches should be removed at a branch fork at least 5 feet and preferably 10 feet below the last sign of streaking in the sapwood (figure 8) Whenever elm branches are pruned during the growing season pruning paint specifically formulated for use on trees should be applied to prevent attraction of elm bark beetles to the wounded trees (Painting tree wounds is generally not recommended except to prevent disease transmission in oaks and elms)

Figure 8 Eradicative pruning of branches infected with DED may be effective if there is adequate length (5 to 10 feet) of clearwood between the infected tissue and the remainder of the crown or if the tree has been properly treated with fungicide (Artwork courtesy of Jim Lockyer USDA Forest Service Radnor PA)

Pruning is more likely to be effective if augmented by systemic injection of fungicides Proper use of fungicides eliminates the need to eradicate all infected tissues from the tree although all dead branches should eventually be removed Whereas pruning alone is not effective against residual infections fungicide injection may be If fungicides are used they should be injected prior to removal of diseased branches The keys to successful eradicative treatment are early detection and prompt treatment

Planting Dutch Elm Disease resistant or tolerant trees Planting trees with resistance or tolerance to DED is a valid management option However selecting only a few cultivars limits the genetic variability of the population This could lead to increased risk of widespread losses if these cultivars are found to be susceptible to tree health problems such as poor adaptation to site air pollution other elm pests or pathogens (such as elm yellows or elm leaf beetle) or even other strains of DED which may eventually develop Thus it is prudent to plant a mixture of suitable cultivars of as many elm genotypes as possible Santamour and Bentz (1995) recently published a checklist and brief description of elm cultivars in North America The only true American elms on that list that are commercially available and have strong evidence of DED tolerance or resistance are the Princeton Elm the American Liberty multi-clone and Independence which is one of the cultivars in the American Liberty multi-clone Two additional American elms Valley Forge and New Harmony were released by the USDA National Arboretum since the Santamour and Bentz listing was prepared These two cultivars which exhibit high tolerance to DED should be available through retail nurseries by 2001

Besides true American elms there are many other hybrid elm crosses and species of elm that have high tolerance or resistance to DED Several of these have attractive form are well suited to urban environments and are readily available (figure 9) Many of these are listed and described by Santamour and Bentz (1995) in the previously mentioned checklist

Figure 9 Cultivars of elm selected for resistance to DED are available This selection of Ulmus japonica demonstrates the potential these elms have as landscape trees (Photo courtesy of Dr Eugene Smalley University of Wisconsin--Madison)

In addition to careful selection of the tree species and cultivar location and spacing are also important to reduce losses from DED When selecting landscape trees and their locations plant a mixture of tree species appropriate to the site In addition to the species diversity consider spacing of the trees Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity

Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and DED fungus to infect high value landscape trees Management is necessary in order to protect urban elms

The most effective management option to reduce both the bark beetle vectors and the DED fungus is sanitation to promptly remove stressed dead and dying elms as previously described However this intensity of treatment is often not feasible

A trap tree method was developed in the 1980s to more cost effectively reduce populations of elm bark beetles Under this method DED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark The bark beetles are attracted to the dying trees but the rapidly drying bark is unsuitable for them to complete their lifecycle and the bark beetle populations are reduced However treated trees may then become hazard trees with high risk of falling and causing personal injury or property damage

Another option in wild areas or natural stands other than accepting losses from DED is to eliminate all elms and manage for alternative species However it is often desirable to retain elms for biodiversity aesthetic economic or other reasons

Deciding Which Management Practices to Use Different management strategies will be applicable depending on whether you are working with a community program or trying to protect individual trees In a community program the objective will be to protect a population of elms Individual landowners however may have no control over what neighbors do with their elms but may want to protect or save their own trees The amount of money an individual or community is able to spend will also vary

Where you have no control over the management of surrounding trees the only options available are treatments to protect or save individual trees Good sanitation practices and disruption of root grafts are necessary on individual properties but these practices alone will not protect a tree from disease transmission by bark beetles from other properties Preventive fungicide injection eradicative pruning and fungicide injection and insecticide treatment are generally the only options available for individual trees

In a community program resources to spend on individual trees may be low but there is more opportunity to manage populations of elms Where there are continuous elms root graft disruption is essential to halt the spread Sanitation is key to reducing beetle and DED populations and is effective Community ordinances can be established to encourage prompt removal of diseased trees and

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

(Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The elm host Native species of North American elms vary in their susceptibility to DED even within species American elm (Ulmus americana L) is generally highly susceptible Winged elm (U alata Michx) September elm (U serotina Sarg) slippery elm (U rubra Muhl) rock elm (U thomasii Sarg) and cedar elm (U crassifolia Nutt) range from susceptible to somewhat resistant No native elms are immune to DED but some individuals or cultivars have a higher tolerance (and thus may recover from or survive with infection) or resistance to DED Many European and Asiatic elms are less susceptible than American elm

In addition to genetic factors present in some cultivars and species physical factors affect tree susceptibility These factors include time of year climatic conditions (such as drought) and vitality of the tree Water conducting elements are most susceptible to infection as they are being produced in the spring thus elms are most susceptible to infection after earliest leafing out to midsummer Trees are less susceptible under drought conditions Vigorously growing trees are generally more susceptible than slower growing trees

The Dutch elm disease fungus DED can be caused by either of two closely related species of fungi Ophiostoma ulmi (Buism) Nannf (formerly called Ceratocystis ulmi) and Ophiostoma novo-ulmi Brasier The latter which is more aggressive in causing disease was recently recognized as being a separate species The DED fungus was first introduced to the US on diseased elm logs from Europe prior to 1930 It is unknown when the more aggressive species became established in the US however it was possibly present as early as the 1940s- 1950s and most likely caused much of the devastating mortality through the 1970s The less aggressive species is becoming increasingly rare in nature and the aggressive species is thought to be responsible for most of the current mortality Although some local resurgence of DED has been observed there is no evidence that it is due to a change in the pathogen Localized resurgence is more likely due to the following (1) a decrease in vigilance in monitoring and sanitation (2) a build-up in populations of the insect vectors or (3) ingrowth of susceptible host trees in the wild

Spread by elm bark beetles Overland spread of DED is closely linked to the life cycles of the native elm bark beetle (Hylurgopinus rufipes Eich) and the smaller European elm bark beetle (Scolytus multistriatus Marsh) (figure 5) Both beetles are attracted to stressed dying or dead elm wood to complete the breeding stage of their life cycle The adult beetles tunnel into the bark and lay their eggs in tunnels (called galleries) in the inner bark The eggs hatch and the larvae feed in the inner bark and sapwood

The larvae mature into adults and emerge from the elm wood If the DED fungus was present in the wood that the beetles infested the fungus produces sticky spores in the beetle galleries Spores of the DED fungus are eaten by or stick to the adult beetles as they emerge from diseased trees Adult beetles then visit healthy trees feed in twig crotches or branch inner bark and introduce the fungus into or near severed wood vessels as they feed

Figure 5 Overland spread of DED is closely tied to the life cycles of the Native elm bark beetle (top) and smaller European elm bark beetle (below) Note that the smaller European elm bark beetle is actually larger

than the native elm bark beetle (Artwork by Julie Martinez Scientific Illustrator St Paul MN)

The importance of the two bark beetle species as vectors of DED varies across the range of elms In northern areas (northern parts of Minnesota Wisconsin Maine New York and New England and most of Canada where winter temperatures below -6deg F are common) the native elm bark beetle is the predominant vector In other parts of North America the smaller European elm bark beetle predominates The life habits of the adults of the two species differ considerably which has implications for management opportunities These differences are described below

Smaller European elm bark beetles overwinter as larvae or adults within the stem of the tree where they hatched They emerge as adults in spring to feed in twig crotches of healthy trees where they can introduce spores of the DED fungus to the crown High numbers of beetles frequently will feed in a single tree resulting in multiple points of infection The cycle is repeated when beetles then seek out diseased and dying wood to breed in throughout the growing season completing two or more generations per year They have the potential to rapidly build up high populations

Adult native elm bark beetles tunnel into the bark on the lower stems of healthy elms to overwinter In spring they emerge to feed in the inner bark of elm branches and small stems before beginning their breeding cycle They repeat their life cycle as previously described They can transmit the DED fungus to healthy trees during the construction of overwintering sites in fall or more commonly during feeding in spring

Once the DED fungus is introduced into the upper crown of healthy elms by bark beetles it slowly moves downward killing the

branch as it goes Disease progression may occur rapidly killing the tree by the end of the growing season or may progress gradually over a period of two or more years It is also possible that the tree may recover The success and rate of progression within the tree depends on tree size time and location of infection in the tree climatic conditions and response of the host tree Spread through grafted roots Roots of the same or closely related tree species growing near each other often cross each other in the soil and eventually fuse (become grafted) to each other

The DED fungus can move from infected trees to adjacent trees through these grafted roots Infections that occur through root grafts can spread very rapidly throughout the tree as the fungus is carried upward in the sapstream Root graft spread of DED is a very significant cause of tree death in urban areas where elms are closely spaced (figure 6)

Figure 6 Where elms are closely spaced the Dutch elm disease fungus may move down a row of trees through grafted roots Removing trees without breaking root grafts may not keep the fungus from moving into adjacent trees (Photo courtesy of Dr Joseph OBrien USDA Forest Service St Paul MN)

Managing Dutch Elm Disease

DED is managed by interrupting the disease cycle The most effective means of breaking the cycle is early and thorough sanitation to limit the population of the insects that transmit the fungus from tree to tree Other useful means of affecting the disease cycle include using insecticides to kill the insect vector breaking root grafts between trees injecting individual trees with fungicides to prevent or halt the fungus pruning out early infections and planting DED tolerant or resistant elm cultivars or other tree species

Sanitation to reduce insect vectors Many communities have been able to maintain a healthy population of mature elms through a vigilant program of identification and removal of diseased elms and systematic pruning of weakened dying or dead branches Sanitation by prompt removal of diseased trees or branches reduces breeding sites for elm bark beetles and eliminates the source of the DED fungus To be completely effective in interrupting the spread of the disease by elm bark beetles stems and branches of DED infected trees must be de-barked destroyed or utilized before the bark beetles emerge During the growing season removal should be completed within 2 to 3 weeks of detection During the dormant season removal should be completed before April when overwintering beetles may begin to emerge

Wood from infected trees can be destroyed by chipping burning or burying Wood may be retained for use as firewood or sawlogs if it is de-barked or covered from April 15th to October 15th with 4 to 6 mil plastic The edges of the cover must be buried or sealed to the ground If it is impossible to destroy all elm wood before the beetles emerge the wood can be sprayed with a registered insecticide until disposal is possible If insecticides are used consider potential exposure to chemical residues when burning or handling the treated wood Many communities have regulations on the removal of diseased elms and storage of elm firewood make sure your activities comply with local regulations

Insecticides to kill insect vectors In areas where the native elm bark beetle is the principal vector sanitation may be augmented by applying a registered insecticide to the lower stem of healthy elms in late summer to early fall (ie at the first sign of autumn leaf color change) to kill adult beetles as they prepare overwintering sites In areas where the smaller European elm bark beetle are common spring feeding in twig crotches can be prevented by spraying the crowns of elm trees with a registered insecticide However this may not be a preferred treatment method because of the difficulty in getting thorough coverage of all susceptible twig tissue the risk of insecticide drift and exposure and high expense

Insecticide registrations and recommendations are frequently updated and may vary considerably between states Cooperative Extension Services at land grant colleges and certified arborists are able to provide current insecticide recommendations

Disruption of root grafts Large trees within 25 to 50 feet of each other are likely to have root grafts Breaking root grafts between infected trees and adjacent healthy trees is an important means to prevent movement of the fungus into the healthy trees Root grafts should also be disrupted between the healthy tree adjacent to a diseased tree and the next healthy tree It may even be desirable to sever grafts between very valuable trees before DED is observed in the vicinity as a proactive measure

Root graft disruption should be completed before the infected trees are removed Otherwise the transpirational pull from healthy trees will rapidly draw in the contents of diseased trees root system when the vascular tension on the roots of the diseased tree is released by severing the stem Root graft disruption can be accomplished by use of a vibratory plow or any trenching machine equipped with the longest blade available (preferably five-feet long but at least three-feet long) Biocidal soil fumigants may also be used to kill root

grafts if no other alternatives are available However these chemicals are generally restricted use pesticides and may only be applied by professional pesticide applicators In addition biocidal chemicals may not be effective if soil temperatures are below 50 degF Injecting elms with fungicide Certain fungicides when properly injected are effective in protecting elm trees from infection via beetle transmission This treatment is expensive and must be repeated every one to three seasons thus it is appropriate only for high value or historically important trees The treatment itself also may pose risks to the health of the tree

Figure 7

Macroinjection of fungicide into the root flare of an elm tree (Photo courtesy of Mark Stennes certified arborist St Paul MN)

In order to be effective the fungicide must be present at adequate concentration at all potential points of infection Thus the dosage and means of application are critical to success The injection of chemical into root flares in large volumes of water (macroinjection) provides thorough distribution of chemical in the crown (figure 7) Microinjection (injection of small volumes of concentrated chemical) is also an option although its efficacy compared to macroinjection has not been thoroughly researched Preferably injections should be done soon after the earliest leaves have fully expanded but may be done from then to the end of the growing season Label rates of concentration for chemical application are updated to reflect the most recent findings on effectiveness always follow the current label

Harmful effects of fungicide injection have sometimes been reported and include occasional leaf scorching or loss Elms generally recover from this damage Also drilling injection holes results in wounding which if repeated annually may eventually result in significant discoloration and decay Following fungicide injection with a flush of clean water can reduce damage to the cambium Some chemicals are able to protect trees for up to three seasons thus minimizing the frequency of treatments

Several fungicides are registered for injection to prevent DED infection These chemicals vary in duration of protective effects means of application risk of damage to the tree documentation of effectiveness and cost Certified arborists or Cooperative Extension Services at land grant colleges are able to provide current recommendations on product availability and effectiveness Eradicating Dutch elm disease from newly infected trees If a new crown infection of DED is detected early enough there is opportunity to save a tree through pruning fungicide injection or both Eradicative treatment is not possible on trees that have become infected via root graft transmission Pruning which can literally eradicate the fungus from the tree by removing it has a high probability of saving a newly infected tree that has less than 5 of its crown affected To be a candidate for eradicative pruning the infection must be a new infection (not a residual infection from the previous season) and be present only in the upper crown (not yet present in the main stem) Since infection may be more advanced than symptoms indicate it is important to peel off the bark of infected branches and locate the staining which indicates the presence of the fungus All infected branches should be removed at a branch fork at least 5 feet and preferably 10 feet below the last sign of streaking in the sapwood (figure 8) Whenever elm branches are pruned during the growing season pruning paint specifically formulated for use on trees should be applied to prevent attraction of elm bark beetles to the wounded trees (Painting tree wounds is generally not recommended except to prevent disease transmission in oaks and elms)

Figure 8 Eradicative pruning of branches infected with DED may be effective if there is adequate length (5 to 10 feet) of clearwood between the infected tissue and the remainder of the crown or if the tree has been properly treated with fungicide (Artwork courtesy of Jim Lockyer USDA Forest Service Radnor PA)

Pruning is more likely to be effective if augmented by systemic injection of fungicides Proper use of fungicides eliminates the need to eradicate all infected tissues from the tree although all dead branches should eventually be removed Whereas pruning alone is not effective against residual infections fungicide injection may be If fungicides are used they should be injected prior to removal of diseased branches The keys to successful eradicative treatment are early detection and prompt treatment

Planting Dutch Elm Disease resistant or tolerant trees Planting trees with resistance or tolerance to DED is a valid management option However selecting only a few cultivars limits the genetic variability of the population This could lead to increased risk of widespread losses if these cultivars are found to be susceptible to tree health problems such as poor adaptation to site air pollution other elm pests or pathogens (such as elm yellows or elm leaf beetle) or even other strains of DED which may eventually develop Thus it is prudent to plant a mixture of suitable cultivars of as many elm genotypes as possible Santamour and Bentz (1995) recently published a checklist and brief description of elm cultivars in North America The only true American elms on that list that are commercially available and have strong evidence of DED tolerance or resistance are the Princeton Elm the American Liberty multi-clone and Independence which is one of the cultivars in the American Liberty multi-clone Two additional American elms Valley Forge and New Harmony were released by the USDA National Arboretum since the Santamour and Bentz listing was prepared These two cultivars which exhibit high tolerance to DED should be available through retail nurseries by 2001

Besides true American elms there are many other hybrid elm crosses and species of elm that have high tolerance or resistance to DED Several of these have attractive form are well suited to urban environments and are readily available (figure 9) Many of these are listed and described by Santamour and Bentz (1995) in the previously mentioned checklist

Figure 9 Cultivars of elm selected for resistance to DED are available This selection of Ulmus japonica demonstrates the potential these elms have as landscape trees (Photo courtesy of Dr Eugene Smalley University of Wisconsin--Madison)

In addition to careful selection of the tree species and cultivar location and spacing are also important to reduce losses from DED When selecting landscape trees and their locations plant a mixture of tree species appropriate to the site In addition to the species diversity consider spacing of the trees Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity

Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and DED fungus to infect high value landscape trees Management is necessary in order to protect urban elms

The most effective management option to reduce both the bark beetle vectors and the DED fungus is sanitation to promptly remove stressed dead and dying elms as previously described However this intensity of treatment is often not feasible

A trap tree method was developed in the 1980s to more cost effectively reduce populations of elm bark beetles Under this method DED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark The bark beetles are attracted to the dying trees but the rapidly drying bark is unsuitable for them to complete their lifecycle and the bark beetle populations are reduced However treated trees may then become hazard trees with high risk of falling and causing personal injury or property damage

Another option in wild areas or natural stands other than accepting losses from DED is to eliminate all elms and manage for alternative species However it is often desirable to retain elms for biodiversity aesthetic economic or other reasons

Deciding Which Management Practices to Use Different management strategies will be applicable depending on whether you are working with a community program or trying to protect individual trees In a community program the objective will be to protect a population of elms Individual landowners however may have no control over what neighbors do with their elms but may want to protect or save their own trees The amount of money an individual or community is able to spend will also vary

Where you have no control over the management of surrounding trees the only options available are treatments to protect or save individual trees Good sanitation practices and disruption of root grafts are necessary on individual properties but these practices alone will not protect a tree from disease transmission by bark beetles from other properties Preventive fungicide injection eradicative pruning and fungicide injection and insecticide treatment are generally the only options available for individual trees

In a community program resources to spend on individual trees may be low but there is more opportunity to manage populations of elms Where there are continuous elms root graft disruption is essential to halt the spread Sanitation is key to reducing beetle and DED populations and is effective Community ordinances can be established to encourage prompt removal of diseased trees and

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

branch as it goes Disease progression may occur rapidly killing the tree by the end of the growing season or may progress gradually over a period of two or more years It is also possible that the tree may recover The success and rate of progression within the tree depends on tree size time and location of infection in the tree climatic conditions and response of the host tree Spread through grafted roots Roots of the same or closely related tree species growing near each other often cross each other in the soil and eventually fuse (become grafted) to each other

The DED fungus can move from infected trees to adjacent trees through these grafted roots Infections that occur through root grafts can spread very rapidly throughout the tree as the fungus is carried upward in the sapstream Root graft spread of DED is a very significant cause of tree death in urban areas where elms are closely spaced (figure 6)

Figure 6 Where elms are closely spaced the Dutch elm disease fungus may move down a row of trees through grafted roots Removing trees without breaking root grafts may not keep the fungus from moving into adjacent trees (Photo courtesy of Dr Joseph OBrien USDA Forest Service St Paul MN)

Managing Dutch Elm Disease

DED is managed by interrupting the disease cycle The most effective means of breaking the cycle is early and thorough sanitation to limit the population of the insects that transmit the fungus from tree to tree Other useful means of affecting the disease cycle include using insecticides to kill the insect vector breaking root grafts between trees injecting individual trees with fungicides to prevent or halt the fungus pruning out early infections and planting DED tolerant or resistant elm cultivars or other tree species

Sanitation to reduce insect vectors Many communities have been able to maintain a healthy population of mature elms through a vigilant program of identification and removal of diseased elms and systematic pruning of weakened dying or dead branches Sanitation by prompt removal of diseased trees or branches reduces breeding sites for elm bark beetles and eliminates the source of the DED fungus To be completely effective in interrupting the spread of the disease by elm bark beetles stems and branches of DED infected trees must be de-barked destroyed or utilized before the bark beetles emerge During the growing season removal should be completed within 2 to 3 weeks of detection During the dormant season removal should be completed before April when overwintering beetles may begin to emerge

Wood from infected trees can be destroyed by chipping burning or burying Wood may be retained for use as firewood or sawlogs if it is de-barked or covered from April 15th to October 15th with 4 to 6 mil plastic The edges of the cover must be buried or sealed to the ground If it is impossible to destroy all elm wood before the beetles emerge the wood can be sprayed with a registered insecticide until disposal is possible If insecticides are used consider potential exposure to chemical residues when burning or handling the treated wood Many communities have regulations on the removal of diseased elms and storage of elm firewood make sure your activities comply with local regulations

Insecticides to kill insect vectors In areas where the native elm bark beetle is the principal vector sanitation may be augmented by applying a registered insecticide to the lower stem of healthy elms in late summer to early fall (ie at the first sign of autumn leaf color change) to kill adult beetles as they prepare overwintering sites In areas where the smaller European elm bark beetle are common spring feeding in twig crotches can be prevented by spraying the crowns of elm trees with a registered insecticide However this may not be a preferred treatment method because of the difficulty in getting thorough coverage of all susceptible twig tissue the risk of insecticide drift and exposure and high expense

Insecticide registrations and recommendations are frequently updated and may vary considerably between states Cooperative Extension Services at land grant colleges and certified arborists are able to provide current insecticide recommendations

Disruption of root grafts Large trees within 25 to 50 feet of each other are likely to have root grafts Breaking root grafts between infected trees and adjacent healthy trees is an important means to prevent movement of the fungus into the healthy trees Root grafts should also be disrupted between the healthy tree adjacent to a diseased tree and the next healthy tree It may even be desirable to sever grafts between very valuable trees before DED is observed in the vicinity as a proactive measure

Root graft disruption should be completed before the infected trees are removed Otherwise the transpirational pull from healthy trees will rapidly draw in the contents of diseased trees root system when the vascular tension on the roots of the diseased tree is released by severing the stem Root graft disruption can be accomplished by use of a vibratory plow or any trenching machine equipped with the longest blade available (preferably five-feet long but at least three-feet long) Biocidal soil fumigants may also be used to kill root

grafts if no other alternatives are available However these chemicals are generally restricted use pesticides and may only be applied by professional pesticide applicators In addition biocidal chemicals may not be effective if soil temperatures are below 50 degF Injecting elms with fungicide Certain fungicides when properly injected are effective in protecting elm trees from infection via beetle transmission This treatment is expensive and must be repeated every one to three seasons thus it is appropriate only for high value or historically important trees The treatment itself also may pose risks to the health of the tree

Figure 7

Macroinjection of fungicide into the root flare of an elm tree (Photo courtesy of Mark Stennes certified arborist St Paul MN)

In order to be effective the fungicide must be present at adequate concentration at all potential points of infection Thus the dosage and means of application are critical to success The injection of chemical into root flares in large volumes of water (macroinjection) provides thorough distribution of chemical in the crown (figure 7) Microinjection (injection of small volumes of concentrated chemical) is also an option although its efficacy compared to macroinjection has not been thoroughly researched Preferably injections should be done soon after the earliest leaves have fully expanded but may be done from then to the end of the growing season Label rates of concentration for chemical application are updated to reflect the most recent findings on effectiveness always follow the current label

Harmful effects of fungicide injection have sometimes been reported and include occasional leaf scorching or loss Elms generally recover from this damage Also drilling injection holes results in wounding which if repeated annually may eventually result in significant discoloration and decay Following fungicide injection with a flush of clean water can reduce damage to the cambium Some chemicals are able to protect trees for up to three seasons thus minimizing the frequency of treatments

Several fungicides are registered for injection to prevent DED infection These chemicals vary in duration of protective effects means of application risk of damage to the tree documentation of effectiveness and cost Certified arborists or Cooperative Extension Services at land grant colleges are able to provide current recommendations on product availability and effectiveness Eradicating Dutch elm disease from newly infected trees If a new crown infection of DED is detected early enough there is opportunity to save a tree through pruning fungicide injection or both Eradicative treatment is not possible on trees that have become infected via root graft transmission Pruning which can literally eradicate the fungus from the tree by removing it has a high probability of saving a newly infected tree that has less than 5 of its crown affected To be a candidate for eradicative pruning the infection must be a new infection (not a residual infection from the previous season) and be present only in the upper crown (not yet present in the main stem) Since infection may be more advanced than symptoms indicate it is important to peel off the bark of infected branches and locate the staining which indicates the presence of the fungus All infected branches should be removed at a branch fork at least 5 feet and preferably 10 feet below the last sign of streaking in the sapwood (figure 8) Whenever elm branches are pruned during the growing season pruning paint specifically formulated for use on trees should be applied to prevent attraction of elm bark beetles to the wounded trees (Painting tree wounds is generally not recommended except to prevent disease transmission in oaks and elms)

Figure 8 Eradicative pruning of branches infected with DED may be effective if there is adequate length (5 to 10 feet) of clearwood between the infected tissue and the remainder of the crown or if the tree has been properly treated with fungicide (Artwork courtesy of Jim Lockyer USDA Forest Service Radnor PA)

Pruning is more likely to be effective if augmented by systemic injection of fungicides Proper use of fungicides eliminates the need to eradicate all infected tissues from the tree although all dead branches should eventually be removed Whereas pruning alone is not effective against residual infections fungicide injection may be If fungicides are used they should be injected prior to removal of diseased branches The keys to successful eradicative treatment are early detection and prompt treatment

Planting Dutch Elm Disease resistant or tolerant trees Planting trees with resistance or tolerance to DED is a valid management option However selecting only a few cultivars limits the genetic variability of the population This could lead to increased risk of widespread losses if these cultivars are found to be susceptible to tree health problems such as poor adaptation to site air pollution other elm pests or pathogens (such as elm yellows or elm leaf beetle) or even other strains of DED which may eventually develop Thus it is prudent to plant a mixture of suitable cultivars of as many elm genotypes as possible Santamour and Bentz (1995) recently published a checklist and brief description of elm cultivars in North America The only true American elms on that list that are commercially available and have strong evidence of DED tolerance or resistance are the Princeton Elm the American Liberty multi-clone and Independence which is one of the cultivars in the American Liberty multi-clone Two additional American elms Valley Forge and New Harmony were released by the USDA National Arboretum since the Santamour and Bentz listing was prepared These two cultivars which exhibit high tolerance to DED should be available through retail nurseries by 2001

Besides true American elms there are many other hybrid elm crosses and species of elm that have high tolerance or resistance to DED Several of these have attractive form are well suited to urban environments and are readily available (figure 9) Many of these are listed and described by Santamour and Bentz (1995) in the previously mentioned checklist

Figure 9 Cultivars of elm selected for resistance to DED are available This selection of Ulmus japonica demonstrates the potential these elms have as landscape trees (Photo courtesy of Dr Eugene Smalley University of Wisconsin--Madison)

In addition to careful selection of the tree species and cultivar location and spacing are also important to reduce losses from DED When selecting landscape trees and their locations plant a mixture of tree species appropriate to the site In addition to the species diversity consider spacing of the trees Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity

Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and DED fungus to infect high value landscape trees Management is necessary in order to protect urban elms

The most effective management option to reduce both the bark beetle vectors and the DED fungus is sanitation to promptly remove stressed dead and dying elms as previously described However this intensity of treatment is often not feasible

A trap tree method was developed in the 1980s to more cost effectively reduce populations of elm bark beetles Under this method DED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark The bark beetles are attracted to the dying trees but the rapidly drying bark is unsuitable for them to complete their lifecycle and the bark beetle populations are reduced However treated trees may then become hazard trees with high risk of falling and causing personal injury or property damage

Another option in wild areas or natural stands other than accepting losses from DED is to eliminate all elms and manage for alternative species However it is often desirable to retain elms for biodiversity aesthetic economic or other reasons

Deciding Which Management Practices to Use Different management strategies will be applicable depending on whether you are working with a community program or trying to protect individual trees In a community program the objective will be to protect a population of elms Individual landowners however may have no control over what neighbors do with their elms but may want to protect or save their own trees The amount of money an individual or community is able to spend will also vary

Where you have no control over the management of surrounding trees the only options available are treatments to protect or save individual trees Good sanitation practices and disruption of root grafts are necessary on individual properties but these practices alone will not protect a tree from disease transmission by bark beetles from other properties Preventive fungicide injection eradicative pruning and fungicide injection and insecticide treatment are generally the only options available for individual trees

In a community program resources to spend on individual trees may be low but there is more opportunity to manage populations of elms Where there are continuous elms root graft disruption is essential to halt the spread Sanitation is key to reducing beetle and DED populations and is effective Community ordinances can be established to encourage prompt removal of diseased trees and

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

grafts if no other alternatives are available However these chemicals are generally restricted use pesticides and may only be applied by professional pesticide applicators In addition biocidal chemicals may not be effective if soil temperatures are below 50 degF Injecting elms with fungicide Certain fungicides when properly injected are effective in protecting elm trees from infection via beetle transmission This treatment is expensive and must be repeated every one to three seasons thus it is appropriate only for high value or historically important trees The treatment itself also may pose risks to the health of the tree

Figure 7

Macroinjection of fungicide into the root flare of an elm tree (Photo courtesy of Mark Stennes certified arborist St Paul MN)

In order to be effective the fungicide must be present at adequate concentration at all potential points of infection Thus the dosage and means of application are critical to success The injection of chemical into root flares in large volumes of water (macroinjection) provides thorough distribution of chemical in the crown (figure 7) Microinjection (injection of small volumes of concentrated chemical) is also an option although its efficacy compared to macroinjection has not been thoroughly researched Preferably injections should be done soon after the earliest leaves have fully expanded but may be done from then to the end of the growing season Label rates of concentration for chemical application are updated to reflect the most recent findings on effectiveness always follow the current label

Harmful effects of fungicide injection have sometimes been reported and include occasional leaf scorching or loss Elms generally recover from this damage Also drilling injection holes results in wounding which if repeated annually may eventually result in significant discoloration and decay Following fungicide injection with a flush of clean water can reduce damage to the cambium Some chemicals are able to protect trees for up to three seasons thus minimizing the frequency of treatments

Several fungicides are registered for injection to prevent DED infection These chemicals vary in duration of protective effects means of application risk of damage to the tree documentation of effectiveness and cost Certified arborists or Cooperative Extension Services at land grant colleges are able to provide current recommendations on product availability and effectiveness Eradicating Dutch elm disease from newly infected trees If a new crown infection of DED is detected early enough there is opportunity to save a tree through pruning fungicide injection or both Eradicative treatment is not possible on trees that have become infected via root graft transmission Pruning which can literally eradicate the fungus from the tree by removing it has a high probability of saving a newly infected tree that has less than 5 of its crown affected To be a candidate for eradicative pruning the infection must be a new infection (not a residual infection from the previous season) and be present only in the upper crown (not yet present in the main stem) Since infection may be more advanced than symptoms indicate it is important to peel off the bark of infected branches and locate the staining which indicates the presence of the fungus All infected branches should be removed at a branch fork at least 5 feet and preferably 10 feet below the last sign of streaking in the sapwood (figure 8) Whenever elm branches are pruned during the growing season pruning paint specifically formulated for use on trees should be applied to prevent attraction of elm bark beetles to the wounded trees (Painting tree wounds is generally not recommended except to prevent disease transmission in oaks and elms)

Figure 8 Eradicative pruning of branches infected with DED may be effective if there is adequate length (5 to 10 feet) of clearwood between the infected tissue and the remainder of the crown or if the tree has been properly treated with fungicide (Artwork courtesy of Jim Lockyer USDA Forest Service Radnor PA)

Pruning is more likely to be effective if augmented by systemic injection of fungicides Proper use of fungicides eliminates the need to eradicate all infected tissues from the tree although all dead branches should eventually be removed Whereas pruning alone is not effective against residual infections fungicide injection may be If fungicides are used they should be injected prior to removal of diseased branches The keys to successful eradicative treatment are early detection and prompt treatment

Planting Dutch Elm Disease resistant or tolerant trees Planting trees with resistance or tolerance to DED is a valid management option However selecting only a few cultivars limits the genetic variability of the population This could lead to increased risk of widespread losses if these cultivars are found to be susceptible to tree health problems such as poor adaptation to site air pollution other elm pests or pathogens (such as elm yellows or elm leaf beetle) or even other strains of DED which may eventually develop Thus it is prudent to plant a mixture of suitable cultivars of as many elm genotypes as possible Santamour and Bentz (1995) recently published a checklist and brief description of elm cultivars in North America The only true American elms on that list that are commercially available and have strong evidence of DED tolerance or resistance are the Princeton Elm the American Liberty multi-clone and Independence which is one of the cultivars in the American Liberty multi-clone Two additional American elms Valley Forge and New Harmony were released by the USDA National Arboretum since the Santamour and Bentz listing was prepared These two cultivars which exhibit high tolerance to DED should be available through retail nurseries by 2001

Besides true American elms there are many other hybrid elm crosses and species of elm that have high tolerance or resistance to DED Several of these have attractive form are well suited to urban environments and are readily available (figure 9) Many of these are listed and described by Santamour and Bentz (1995) in the previously mentioned checklist

Figure 9 Cultivars of elm selected for resistance to DED are available This selection of Ulmus japonica demonstrates the potential these elms have as landscape trees (Photo courtesy of Dr Eugene Smalley University of Wisconsin--Madison)

In addition to careful selection of the tree species and cultivar location and spacing are also important to reduce losses from DED When selecting landscape trees and their locations plant a mixture of tree species appropriate to the site In addition to the species diversity consider spacing of the trees Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity

Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and DED fungus to infect high value landscape trees Management is necessary in order to protect urban elms

The most effective management option to reduce both the bark beetle vectors and the DED fungus is sanitation to promptly remove stressed dead and dying elms as previously described However this intensity of treatment is often not feasible

A trap tree method was developed in the 1980s to more cost effectively reduce populations of elm bark beetles Under this method DED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark The bark beetles are attracted to the dying trees but the rapidly drying bark is unsuitable for them to complete their lifecycle and the bark beetle populations are reduced However treated trees may then become hazard trees with high risk of falling and causing personal injury or property damage

Another option in wild areas or natural stands other than accepting losses from DED is to eliminate all elms and manage for alternative species However it is often desirable to retain elms for biodiversity aesthetic economic or other reasons

Deciding Which Management Practices to Use Different management strategies will be applicable depending on whether you are working with a community program or trying to protect individual trees In a community program the objective will be to protect a population of elms Individual landowners however may have no control over what neighbors do with their elms but may want to protect or save their own trees The amount of money an individual or community is able to spend will also vary

Where you have no control over the management of surrounding trees the only options available are treatments to protect or save individual trees Good sanitation practices and disruption of root grafts are necessary on individual properties but these practices alone will not protect a tree from disease transmission by bark beetles from other properties Preventive fungicide injection eradicative pruning and fungicide injection and insecticide treatment are generally the only options available for individual trees

In a community program resources to spend on individual trees may be low but there is more opportunity to manage populations of elms Where there are continuous elms root graft disruption is essential to halt the spread Sanitation is key to reducing beetle and DED populations and is effective Community ordinances can be established to encourage prompt removal of diseased trees and

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Planting Dutch Elm Disease resistant or tolerant trees Planting trees with resistance or tolerance to DED is a valid management option However selecting only a few cultivars limits the genetic variability of the population This could lead to increased risk of widespread losses if these cultivars are found to be susceptible to tree health problems such as poor adaptation to site air pollution other elm pests or pathogens (such as elm yellows or elm leaf beetle) or even other strains of DED which may eventually develop Thus it is prudent to plant a mixture of suitable cultivars of as many elm genotypes as possible Santamour and Bentz (1995) recently published a checklist and brief description of elm cultivars in North America The only true American elms on that list that are commercially available and have strong evidence of DED tolerance or resistance are the Princeton Elm the American Liberty multi-clone and Independence which is one of the cultivars in the American Liberty multi-clone Two additional American elms Valley Forge and New Harmony were released by the USDA National Arboretum since the Santamour and Bentz listing was prepared These two cultivars which exhibit high tolerance to DED should be available through retail nurseries by 2001

Besides true American elms there are many other hybrid elm crosses and species of elm that have high tolerance or resistance to DED Several of these have attractive form are well suited to urban environments and are readily available (figure 9) Many of these are listed and described by Santamour and Bentz (1995) in the previously mentioned checklist

Figure 9 Cultivars of elm selected for resistance to DED are available This selection of Ulmus japonica demonstrates the potential these elms have as landscape trees (Photo courtesy of Dr Eugene Smalley University of Wisconsin--Madison)

In addition to careful selection of the tree species and cultivar location and spacing are also important to reduce losses from DED When selecting landscape trees and their locations plant a mixture of tree species appropriate to the site In addition to the species diversity consider spacing of the trees Future problems with root grafts can be avoided by carefully selecting planting location and maximizing tree species diversity

Trees in Natural Stands or Wild Areas Infected elms in wild areas and natural stands that are within or near urban areas often serve as a reservoir of elm bark beetles and DED fungus to infect high value landscape trees Management is necessary in order to protect urban elms

The most effective management option to reduce both the bark beetle vectors and the DED fungus is sanitation to promptly remove stressed dead and dying elms as previously described However this intensity of treatment is often not feasible

A trap tree method was developed in the 1980s to more cost effectively reduce populations of elm bark beetles Under this method DED infected elms which are still living are treated with an herbicide that kills the tree quickly and promotes rapid drying out of the bark The bark beetles are attracted to the dying trees but the rapidly drying bark is unsuitable for them to complete their lifecycle and the bark beetle populations are reduced However treated trees may then become hazard trees with high risk of falling and causing personal injury or property damage

Another option in wild areas or natural stands other than accepting losses from DED is to eliminate all elms and manage for alternative species However it is often desirable to retain elms for biodiversity aesthetic economic or other reasons

Deciding Which Management Practices to Use Different management strategies will be applicable depending on whether you are working with a community program or trying to protect individual trees In a community program the objective will be to protect a population of elms Individual landowners however may have no control over what neighbors do with their elms but may want to protect or save their own trees The amount of money an individual or community is able to spend will also vary

Where you have no control over the management of surrounding trees the only options available are treatments to protect or save individual trees Good sanitation practices and disruption of root grafts are necessary on individual properties but these practices alone will not protect a tree from disease transmission by bark beetles from other properties Preventive fungicide injection eradicative pruning and fungicide injection and insecticide treatment are generally the only options available for individual trees

In a community program resources to spend on individual trees may be low but there is more opportunity to manage populations of elms Where there are continuous elms root graft disruption is essential to halt the spread Sanitation is key to reducing beetle and DED populations and is effective Community ordinances can be established to encourage prompt removal of diseased trees and

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

prevent the storage of elm wood with bark intact Education will help citizens understand the importance and benefits of working together to manage DED As resources allow preventive treatment eradicative treatment and insecticides can be used to augment a program If you are working with a community with a significant elm resource become familiar with the literature listed below and with what has worked well in other communities

The impact of DED on our urban forests has been massive Despite the losses elms should and will continue to be a component of many urban forests We have an opportunity to consider what trees will compose the future urban forest and we can learn from the past Landowners and communities can and should choose carefully what types of trees to plant and where to plant them

Bibliography

bull Allison J R and G F Gregory 1979 How to Save Dutch Elm Diseased Trees by Pruning USDA FS publication NA-GR-9 bull Ascerno M E and R P Wawrzynski 1993 Native Elm Bark Beetle Control Minnesota Extension Service Publication FS-1420-GO bull Becker H 1996 New American Elms Restore Stately Trees 1996 Agricultural Research 44 (7)4-8 bull Brasier C M 1991 Ophiostoma novo-ulmi sp nov Causative Agent of Current Dutch Elm Disease Pandemics Mycopathologia 115151-161 bull Gibson L P A R Hastings and L A LaMadeleine 1981 How To Differentiate Dutch Elm Disease From Elm Phloem Necrosis USDA-FS publication

NA-FBP-11 bull Hanish M A H D Brown and E A Brown (Eds) 1983 Dutch Elm Disease Management Guide USDA-FS and USDA Extension Service Bulletin One bull Lanier G N 1988 Therapy for Dutch Elm Disease Journal of Arboriculture 14(9)229-232 bull Lanier G N 1989 Trap Trees for Control of Dutch Elm Disease Journal of Arboriculture 15(5)105-111 bull National Park Service 1993 Bacterial Leaf Scorch of Landscape Trees Center for Urban Ecology Information Bulletin bull Santamour Frank S Jr and Susan E Bentz 1995 Updated Checklist of Elm (Ulmus) Cultivars for Use in North America Journal of Arboriculture 21

(3)122-131 bull Schreiber R R and J W Peacock 1979 Dutch Elm Disease and Its Control USDA-FS Agriculture Information Bulletin No 193 bull Stennes M A and D W French 1987 Distribution and Retention of Thiabendazole Hypophosphite and Carbendazim Phosphate Injected into Mature

American Elms Phytopathology 77707-712 bull Stipes R J and R J Campana eds 1981 Compendium of Elm Diseases Published by the American Phytopathological Society 96 pp

Northeastern Area - State amp Private Forestry Offices Headquarters Northeastern Area State amp Private Forestry USDA Forest Service 100 Matsonford Road 5 Radnor Corporate Center Suite 200 Radnor PA 19087-8775 Durham Field Office Northeastern Area State amp Private Forestry USDA Forest Service Louis C Wyman Forest Sciences Laboratory PO Box 640 Durham NH 03824-9799 Morgantown Field Office Northeastern Area State amp Private Forestry USDA Forest Service 180 Canfield Street Morgantown WV 26505-3101 St Paul Field Office Northeastern Area State amp Private Forestry USDA Forest Service 1993 Folwell Avenue St Paul MN 55108-1099

Pesticide Precautionary Statement Pesticides used improperly can be injurious to humans animals and plants Follow label directions and heed all precautions on the labels Store all pesticides in original containers out of reach of children and foodstuffs Apply pesticides selectively and carefully Do not apply a pesticide when there is danger of drift to other areas After handling a pesticide do not eat drink or smoke until you have washed Dispose of empty pesticide containers properly It is difficult to remove all traces of a herbicide (weed killer) from equipment Therefore to prevent injury to desirable plants do not use the same equipment for insecticides that you use for herbicides NOTE Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

MR-03765 1993

History of Dutch Elm Disease in Minnesota

Management of Dutch elm disease People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus

From the very beginning of the impact of Dutch elm disease in the United States professionals (ie scientists) and amateurs have competed in the search for a magic cure Miraculous cures have been publicized to the extent that much of the ldquotried and truerdquo basics of dealing with the disease have been shoved aside and even ridiculed The unfortunate truth has been repeatedly supported by the failures of these ldquomiraclerdquo cures the recommended control measures which are effective can be accomplished only with hard work and money

No Magic Bullets People continue to search for that magic compound which will cure even diseased trees completely colonized by the fungus Tremendous sums of money have been spent on fake cures treatments which were known by those knowledgeable about tree diseases to be of no value Often these cures some of which receive national front page news coverage are proposed by people who have little or no understanding of the fungus and the disease Promotions by non-pathologists are not only publicized but are often also financially supported by the public

The major attention that these magic cures often receive is to the detriment of continuing education of the public on the proven control program Not only is money often spent foolishly but the treated trees are lost as well

Despite all the efforts expended searching for an exciting new effective technique for controlling Dutch elm disease the basic approach known for years remains the best The simple answer to the control of Dutch elm disease is sanitation

Sanitation includes detection and destruction of all dead and dying elm trees be they American red Siberian or any kind The notion that Siberian elms are resistant which they are and thus do not serve as sources of infested beetles is nonsense The idea that every tree had to be diagnosed in the laboratory before it could be condemned was expensive delaying and led to further spread of the fungus The ldquopressuresrdquo brought to bear on behalf of some elms because of their prominence or their ownership by a prominent citizen were also disastrous to neighboring elms Sanitation programs were constantly being blocked and slowed by individuals who proclaimed to be concerned about our environment

Sanitation was further encumbered by the well-meaning Pollution Control Agency which prohibited burning despite that being the most expeditious way to dispose of beetles and beetle environments The efforts to slow Dutch elm disease would have fared much better and cost much less if burning had been allowed Random uncontrolled burning was not what was sought Supervised burning in prescribed locations would have provided great advantages to those fighting Dutch elm disease and

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

any resulting pollution could have been considered a small price to pay The permissible thousands of fireplace fires in a single evening in Minnesotarsquos cities have far more impact on the environment than would have been created with the few fires that were foolishly prevented from being used to burn elm refuse piles

One of the major metropolitan elm disposal sites was fortunate to have accidently gotten around that burning ban It was a site designed to promote the utilization of the elm wood from removed trees Logs branches and brush poured into the site in conformance with magnificent plans to salvage the quality logs for use in a variety of products Unfortunately the amateur managers of the operation found themselves inundated in acres and acres of elm debris with more coming faster than they could manage At one point their equipment couldnrsquot even move when it was in running order Fortunately on a day when the wind was blowing away from St Paul and weather conditions were otherwise favorable a fire started accidently

What would have cost millions of dollars and taken too long for the operators of the site to process was quickly gone The mayor of St Paul and the cityrsquos fire chief apparently decided it was safe to let the fire burn and better to save the money that would have been needed to put it out and to haul the debris to another location The fire which injured no one and had little impact on the environment saved a lot of money It was hard on bark beetles as well

People proposing alternatives to sanitation were failing to understand the basic biology underlying the spread of the Dutch elm disease fungus The fungus spores carried by the two beetle carriers of Ceratocystis ulmi are spores produced in the insect galleries and the fungus is introduced to the galleries by the female beetles as they lay eggs Thus it made little difference whether a tree died of Dutch elm disease or was killed by an automobile a girdling chain or winter injury Any dead or dying elm could harbor beetles and the fungus

In the early stages of the control programs the requirement that laboratory tests confirm that an elm tree had Dutch elm disease delayed removal of hazardous trees In some cases the lab diagnosis was a month or more late On other occasions the samples from a suspected tree were inadequate and though the tree was infected the fungus was not isolated Those trees remained to endanger all elms in their vicinities Laboratory confirmation was not necessary because Dutch elm disease can be diagnosed accurately in the field

Sanitation in addition to detection and tree removal included separation of roots between infected and healthy trees a technique often referred to as root barriers With all the effort put into searching for a cure practically nothing was done to develop a method of preventing movement of the fungus through common root systems In some Minnesota communities circumstantial evidence suggested that as many as 88 percent of all new cases of Dutch elm disease resulted from invasion through common root systems The only known technique for disrupting these common root systems in cities was with the soil sterilant SMDC but this method has not been well researched and doesnrsquot always work

Egg-laying galleries of the European elm bark beetle have a characteristic but macabre appearence They run parallel to the grain of the tree with the larval feeding tunnels at right angles to the main gallery The beetle overwinters as larvae and emerges as an adult around June A second generation can be produced by these adults in late summer or early fall and in some years weather can permit even a third generation to be produced

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

One major Minnesota city discontinued placing barrier chemicals around diseased trees when a study showed that their techniques were ineffective They were ineffective because they were improperly placing the barrier with the chemical applied only from curb to sidewalk The roots of the boulevard elm trees extended much farther and were actually fused in the front yards where no barriers were placed Even with barriers placed all around the diseased tree they sometimes failed because the roots were not killed at all the points of application or because the fungus had already moved into the adjacent tree Mechanical barriers are not a reasonable solution because of buried utilities

An important fact is that an elm infected through its roots can not be saved but a beetle inoculated tree can be through selective pruning if detected early enough

This other form of sanitation pruning can be practiced only in a small percentage of cases Aside from cost the major objections to using this approach on public property is that it is extremely difficult for city foresters to monitor individual trees especially when losing thousands of trees per year It is a viable approach however and elms can be saved very easily by pruning

In University of Minnesota studies over 95 percent of the diseased elms pruned experimentally have been saved The technique prevents the fungus from entering the main stem and in turn the roots of that and neighboring trees Many of the elms supposedly saved by injecting chemicals were probably actually saved by pruning which is part of the recommendation in chemically treating diseased trees

Additional control measures do exist but all are secondary to sanitation When DDT could be used it did provide some additional protection to a population of elms Meth-oxychlor one alternative to DDT does not persist on foliage branches and must be applied in the spring when weather conditions often limit spraying operations It has not been part of

control programs in Minnesota as it is not effective enough to justify the expense Many people also objected to having their houses cars yards and children sprayed Cities that had such programs abandoned them

Systemic Treatments There is a long history of systemic chemical treatments for Dutch elm disease some directed at the elm bark beetle but most directed at the fungus pathogen The earliest systematic attempts were at the Connecticut Agricultural Experiment Station at New Haven in the 1940s

Effective systemic fungicides came along quite late in the epidemic After some unsatisfactory results research in Wisconsin and Minnesota finally determined that Arbotect is effective when used in sufficient amounts and when properly injected Initially the insoluble form of benomyl was announced as an effective fungicide but its results were not impressive Several publications developed by extension services described its use the requirement for rapid distribution the need for pressure equipment and the technique for solubilizing the fungicide with lactic acid Later benomyl was

Selective pruning although expensive and labor intensive can effectively extend the lives of some infected elms Many of the successful chemical interventions may in fact be attributed as much to accompanying pruning as to the use of the chemicals

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

solubilized with phosphoric acid and the latter material the most promising of this series Lignasan BLP was labeled for control of Dutch elm disease Arbotect came a bit later

Despite their efficacy for the control of Dutch elm disease both Lignasan and Arbotect were labeled at rates far below what was needed for effective treatment one-sixth the needed amount of Lignasan and one-third the amount of Arbotect Initial injections were in the main stem above ground and later through severed roots Best results were obtained by below grade or root flare injections which could protect elms for two years and possibly even into a third season Root flare injections have resulted in far better distribution of the chemical within the tree

The products currently labeled and used in the United States are water soluble acid salts of two benzimidazole compounds developed in the 1970s Measured in terms of long-term prophylactic effectiveness in the tree Arbotect 20-S (thiabendazole-hypophosphite) is currently the product of choice by the professional tree care industry The product also has a therapeutic effectiveness if the fungus infection is not systemic the highest label rate is delivered uniformly to all parts of the tree and the symptomatic parts of the tree are subsequently removed

Current research at the University of Minnesota and Virginia Tech with a relatively new fungicide called Alamo (propiconazole) although too preliminary to report suggests that the product may be effective as a therapeutic treatment for diseased elms Prophylactically the product is completely effective against overland transmission in mature trees at least for the short term (one season)

Despite this progress on the chemical front the economics of fungicide injection are entirely against the process except for trees of high value At more than $10 per inch of tree diameter (measured at at a height 54 inches above ground) it is expensive and certainly not logical for entire populations of trees Injection will also not work in elms infected through the roots or when the fungus has already become established in the main stem

It is unfortunate that the majority of elms injected with system fungicides were improperly treated Not only were the procedures a waste of money but many homeowners having invested several hundred dollars on the process to save their trees argued that their elms should not be removed even though they constituted a hazard The fungus and beetles profited as a result and the sanitation program lost ground

While systemic fungicide injection was of some value when properly administered there were many other proposed cures for Dutch elm disease which in spite of newspaper stories and self supporting statements were of no value There have in fact been well over 500 and possibly as many as 1000 suggested cures for Dutch elm disease Often people became unbelievably enthusiastic before any substantive evidence on a treatmentrsquos effectiveness became available

Many elms have been treated with substances never even approved as non-hazardous by the Environmental Protection Agency Many which have had EPA approval have erroneously promoted the impression that EPA approval also means that a proposed fungicide actually works as advertised

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

The EPA has always passed approval only on whether a compound is hazardous The losers in these affairs have been the tree owners paying out good money while still losing their trees

Another negative attached to the proliferation of unproven and ineffective treatments has been how those failures delayed the introduction of an effective chemical control Research at the Sault St Marie Laboratory in Canada found that Dursban (chlorpyrifos) was effective in reducing populations of the native elm bark beetle which is the primary vector in northern Minnesota and much of Canada2 But even with that evidence it was several years before the use of Dursban was recommended in Minnesota It has since become an important part of a control program especially for northern Minnesota2Gardiner LM and Webb DP 1980 Tests of chlorpyrifos for control of the North American elm bark beetle (Hylurgopinus rufipes Eichh) Department of the Environment Canadian Forest Service Sault St Marie Report OndashXndash311

Injection of dozens of biological and chemical compounds have been proposed as magic cures for Dutch elm disease Several have been tried by researchers at the University of Minnesota on the universitys own trees While a few of the compounds produce some degree of control the overwhelming majority have been found worthless Some can even be dangerous to the tree or the individual handling it

In Partnership

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

MR-03765 1993

History of Dutch Elm Disease in Minnesota

The Future for Elms in Minnesota Our tendency has been to acquiesce to ease and convenience which means wersquove planted easily grown easily transplanted species

Minnesota has not lost all of its elms since Dutch elm disease was first found in the state more than 30 years ago While it is likely that many elms in forested areas of the state will be lost including those of any substantial size elms are a tenacious species and will always be with us We just wonrsquot have as many of the large specimens The cities however face a different scenario and any community that has good judgement will be able to keep many of its elms

A reasonable program of management can continue to maintain low losses and preserve a substantial portion of our shade tree elms The management program is a wise investment because the absence of any effort to stop Dutch elm disease will result in dead trees which still must be removed

An argument can be made that a community actually saves money by keeping the elms it has for as long as it is able Cities should appreciate that it takes decades for newly planted replacement trees to reach the stature and beauty of our existing residual elms And the new trees will have their own problems including susceptibility to their own diseases Finally for the very reason that so many elms were planted in the first place we have to acknowledge that few other tree species are as beautiful and acceptable in as many respects for a shade tree

The choice of replacement trees is surprising in some respects Itrsquos understandable that we are planting more ash (26 percent) trees than any other single species because this tree is cheap to produce easily transplanted and when young reasonably attractive But older ash are not so attractive they lose their leaves early in fall and are late producing leaves in spring Some varieties of ash have had a high rate of mortality and we now have two serious diseases of ash to contend with ash yellows and Verticillium wilt

Another 38 percent of our new replacement trees are exotics which are not entirely suited for this part of the country They are often prone to disease and insect problems Why plant untested exotics when there are dozens of native species The answer in part is that Minnesotans are not growing all of their own trees A high proportion are being shipped in from other parts of the country

Even species native to Minnesota are not necessarily satisfactory if the seed from which they are grown comes from a distant tree Red maples for example grow over much of the eastern United States from Maine to Florida But maples evolved and adapted to Florida are not likely to survive Minnesotarsquos climate Other species that are being planted also have their own disease problems Potentially up to 20 percent of the honey locusts being planted can be infected by a lethal canker disease

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Why not resistant trees Nothing has been said about resistant varieties of elms When Dutch elm disease was causing tremendous losses in Minnesota in the 1970s was not the time to develop resistant elms a process which takes years The Dutch have been at it for six decades with only minimal success They are still searching for that elm they need

Minnesotarsquos reforestry recommendations were based on planting trees which we know are resistant to Dutch elm disease These include maples hackberries oaks and birches to mention a few There was no question about these trees being resistant to Dutch elm disease and they were suited to our climate

The resistant elms which were available in the early years of the Dutch elm disease epidemic were exactly that resistant but not immune More important they were both not well suited to Minnesota and not comparable to the native elms in stature and beauty Siberian and Chinese elms have resistance to Dutch elm disease fungus but are undesirable species because they are subject to winter injury A not entirely facetious recommendation by this author has been that these trees be pruned at the ground line It is not an uncommon scene in Minnesota to see rows and rows of dying Siberian elms which had been planted as windbreaks along roads and around farmersrsquo fields Once established they can become a problem because of their heavy seeding habit

Now is the time to choose carefully and wisely as we select the tree species we plant to renew our urban forests Thus far this has not been

done Our tendency has been to acquiesce to ease and convenience the translation of which means wersquove planted easily grown easily transplanted species Unfortunately this has led to planting too many ash trees too many honey locusts and too many little leaf lindens There are other choices

Is there a place for the elm in the future The answer is a very definite yes There are resistant elms more recently developed which have more desirable characteristics and these are now being evaluated in Minnesota We should consider keeping the American elm in our landscape As Dutch elm disease becomes less abundant and possibly if the nonaggressive strain becomes more common (in 1977 only 8 percent of 1124 isolates were nonaggressive) the American elm might be replanted in some locations It should never be planted as abundantly as was done by our forefathers but it should be a part of our landscape plans

In Partnership

Elmrsquos of any variety do little more than harbor the fungus and the beetles which spread it The only appropriate use for so-called ldquoresistantrdquo varieties may be as firewood or mulch chips

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Oak Wilt in Minnesota David W French Jennifer Juzwik

Copyright copy 2002 Regents of the University of Minnesota All rights reserved

Oak wilt caused by a fungus Ceratocystis fagacearum is responsible for killing large numbers of oaks annually in Minnesota Oaks are undoubtedly the most valuable and plentiful of our shade trees In contrast to Dutch elm disease which has been very difficult to control oak wilt can be more readily controlled and this valuable resource saved

Oak wilt present in many of the eastern states is most common in the Upper Midwest including Minnesota It has spread very slowly north to approximately North Branch and St Cloud and west to Mankato

The greatest concentrations are in and adjacent to the seven-county metropolitan area surrounding Minneapolis and St Paul (Figure 1)

Figure 1

SYMPTOMS

Red oaks such as Northern Red Oak and Northern Pin Oak are highly susceptible to infection by the oak wilt fungus (Figure 2) Oak wilt is easily identified in red oaks by the rapid wilting of affected trees After symptoms first appear a red oak will generally wilt completely in two to six weeks The trees wilt from the top of the crown down and individual leaves wilt from leaf tip and margins to the bases turning bronze to brown (Figure 3) Fallen leaves are often green at the base White oaks range in susceptibility from moderate (Bur Oak) to low (White Oak) (Figure 2) Infected white oaks die slowly a branch at a time often surviving for many years Leaf discoloration of affected white oaks resembles autumn colors

Figure 2 The four most common species of oaks in Minnesota

In both red and white oaks the outer ring of springwood vessels will be plugged with brown material (tyloses and gums) and streaks of brown may be obvious on the outside of the wood The vascular discoloration is most easily seen in cross sections of infected branches of white oaks (Figure 3) and less readily observed in affected red oak branches

Figure 3 Left Read Oak leaves in process of wilting Right Cross-section of White Oak branches show discoloration often seen as small dark dots in the wood just under the bark

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

INFECTION PROCESS

The oak wilt fungus spreads in two ways Most new infections are the result of the fungus moving from infected to healthy oaks via grafted root systems which are common Trees as much as 50 feet apart may be grafted together Root grafts may occur occasionally between different species of oaks

The only way that the fungus can cross highways rivers and open fields is by insect vectors primarily by sap beetles of the Family Nitidulidae This spread occurs infrequently but is important as the means by which new oak wilt infection centers are started Sap beetles are commonly attracted to the sporulating mats produced by the fungus between the bark and wood of oak wilt-killed trees These mats are commonly produced between April and late June on red oaks that wilted during the previous summer (Figure 4) This is also the same period of time that red oaks produce large springwood vessels and are particularly susceptible to infection Several species of the same sap beetles are also attracted to fresh wounds on healthy oaks during spring (mid-April to late June) Visitation of such wounds by Ceratocystis fagacearumNtildecontaminated beetles then results in oak wilt infection Oak bark beetles important oak wilt vectors in some parts of the US are not considered important vectors in Minnesota

Figure 4 A sprorulating mat produced during May by the oak wilt fungus between the bark and wood of a tree that wilted during the previous summer The dark area in the center of the mat are pressure pads that crack open the bark

MANAGEMENT STRATEGIES

Stopping spread of the fungus through common root systems is most important and can be done by mechanical barriers using a vibratory plow with a 5-foot blade Barriers in the soil must be positioned outside of trees with the fungus Often two lines are recommended a primary line outside of apparently healthy trees and a secondary barrier outside of every obviously infected tree (Figure 5) The fungus can be in a tree for 2-3 weeks without leaf symptoms appearing Barrier placement requires experience If buried utilities are present the soil sterilant Vapam can be used but it is not nearly as effective as the mechanical barrier

Overland spread by insects can be prevented by following these guidelines on when to prune and when to paint

sect High Risk Period April May and June dont wound or prune If trees are accidentally wounded or pruning is unavoidable cover the wounds immediately-within minutes-with one of the preferred materials such as water-based paint or shellac

sect Low Risk Period July through October On rare occasions-depending on weather conditions and insect populations-infections may occur Covering wounds is optional

sect Safe Period November through March This is the preferred time for pruning since the fungal pathogen and insect vectors are inactive

sect Tree climbing irons should never be used on living oak trees

As further precaution infected red oaks on which spores may form in spring (Figure 4) should be eliminated by debarking burning burying or wrapping and sealing in 4-6 ml plastic until July 1 Experience is needed to detect these trees before spores are produced The spores are carried by the sap beetles to wound oaks during May and June

Logs from wilting or recently wilted trees should not be moved in any form including firewood to areas where oak wilt is not present Oak wilt mats may form on these logs Long distance movement of firewood obtained from such logs has accounted for establishment of oak wilt centers in distant areas that previously had been unaffected by the disease

In high value white oaks systemic injection with propiconazole by qualified arborists may prevent infection of trees adjacent to oak wilt affected ones Propiconazole treatment of white oaks exhibiting early symptoms of oak wilt (less than 30 of crown affected) can also prevent further disease development for at least 2 years

Figure 5 Diagram of root graft barriers around infected trees

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

A PUBLICATION OF THE MINNESOTA DEPARTMENT OF AGRICULTURE

Vibratory Plow with a Five Foot Blade

OAK CONTROLWILT

BARRIERSRO GRAFTOT

Printed on 100 Recycled Paper

FOR

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

FIGURE 2 The four most common species of oak in Minnesota

RED OAK GROUP WHITE OAK GROUP

NorthernRed Oak

NorthernPin Oak

Burr Oak White Oak

ak wilt is responsible for killing more shade trees each year in Minnesota than any other diseasecausing organism or fungus Fortunately it can be successfully controlled if proper measures aretaken Oak wilt caused by a fungus (Ceratocystis fagacearum) attacks the vascular or water-conducting system of oaks located in the outer ring of sapwood just beneath the bark In an attemptto protect itself from the fungus the tree produces gums and tyloses which plug the water conductingvessels Unable to contain the faster fungus the tree ultimately cuts off its water and nutrient supplybetween roots and crown Visible symptoms (wilting and discoloration of leaves) begin at or nearthe treersquos top or branch ends and progress down and in accompanied by rapid defoliation The oakwilt fungus spreads both overland and underground

DO NOT PRUNE IN MAYOR JUNE Overland the oakwilt fungus is spread by picnicbeetles (family Nitidulidae)These small insects can inocu-late a healthy tree only in May orJune and then only when freshwounds are present Although lessthan l0 percent of the oaks dying ofoak wilt are believed to be infectedthis way it is the only way a newpocket of wilt can start Controlfor this type of spread is easy --oak trees should NOT be cut prunedor injured from April 15 to July 1

WHITE OAKSRESISTANT Trees in thewhite oak group are resistant tooak wilt If they become dis-eased they may take severalyears to die or possibly evenrecover Bur oaks are interme-diate in resistance Diagnosisof oak wilt and control recom-mendations in white oaks shouldbe made on an individual basisby a shade tree professional ex-perienced in oak wilt control

RED OAKS SUSCEPTIBLE Trees in the red oak group are highly susceptible to oak wiltand do not recover if infected Once symptoms appear the tree will wilt completely within a fewweeks If other red oaks are nearby steps should be taken immediately to prevent spread into healthytrees When oak wilt symptoms are first noticed in red oaks the fungus has already spread throughoutthe tree and into the roots In fact the fungus often has already infected the root system of adjacenttrees although they may still look healthy because visible symptoms are not yet apparent

FIGURE 1 Oak roots often fuse (graft) forming a commonroot system on wooded sites The oak wilt fungus can spreadfrom infected to healthy oaks through these root grafts

Root transmission is responsible for 90 percent or more of the trees becoming infected from oakwilt Roots of adjacent oaks (of the same species) within 50 feet of each other are often graftedtogether forming a common root system (see figure 1) The oak wilt fungus spreads through adiseased treersquos vascular system down into its own roots then through the root grafts into adjacenttrees infecting them as well What can be done when oak wilt is diagnosed The answer dependson the species of oak

O

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

sketch on the front cover) Its action is similar to that of an electric knife This machine is fast andcreates only a narrow slit in the ground Since earth is not removed backfilling is unnecessary (Boththe vibratory plow and the trencher are typically pulled by large heavy tractors equiped with flotationtires to minimize soil disturbance) This method is generally the most cost-effective

A trencher has a boom or blade with a cutting chain that spins around cutting a trench four to sixinches wide Its action is similar to that of a chainsaw The trenching blade has a tendency to rideup in the soil and care should be taken to ensure it remains extended to its maximum depth Becausea trencher removes earth as it cuts it is significantly slower than a vibratory plow Persons hiringcontractors with trenchers should ask whether the price includes backfilling the trench

CHEMICAL BARRIER POSSIBLE Another option is a chemical barrier using a soilsterilant known as SMDC or Vapam One- to two-inch-diameter holes 18 to 24 inches deep are drilledalong the barrier line at four-inch intervals a Vapam solution is poured into the holes and the holescovered Vapam kills all roots including grass and other plants along a strip about 18 inches wideCommercially Vapam may be used only by companies licensed with the state for pesticideapplication

Whichever barrier method is used underground utility lines must be located in advance

Diseased trees should not be removed until the root graft disruption work is completed if trees wiltedthat same year If Vapam is used infected trees should be left standing for two weeks after applicationRemoving a tree before root systems are separated may actually speed up the spread of oak wilt (NoteTrees which are structurally weak may present a hazard to people and property and immediateremoval may be warranted - if in doubt check with a professional)

EFFECTIVE TRENCHING PROVIDES BARRIERControl involves severing or breaking the root connec-tions between diseased and healthy oaks (root graftbarriers) The most effective barriers are thoseplaced between the first ring of apparentlyhealthy trees adjacent to the infected onesand the next set of healthy trees (calledprimary barriers - see figure 3) Abarrier placed between diseasedand the first apparently healthyoaks (called a secondary bar-rier) may not stop the dis-ease because the oak wiltfungus may already be inthe adjacent ring of treesbut symptoms are not yetvisible To be successfulall roots between infectedand healthy oaks must becut Mechanical barriersinvolve physically cutting theroots with either a trencher ora vibratory plow This work ismost effective when a blade ortrencher at least five feet long isused

A vibratory plow has a shaker attachment that vibrates a 1-inch thick steel blade up and down (see

FIGURE 3 Diagram of barrier placementbetween infected and healthy trees

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

EFFECTIVENESS VARIES Mechanical barriers are the most effective method of stoppingthe spread of oak wilt -- with a success rate approaching 85 percent (with a 5-foot blade) The successrate for chemical barriers is about 55 percent and is recommended only in areas where use of a plowor trencher isnrsquot feasible (inaccessible to plow steep slopes etc) Correctly locating these root graftbarriers is extremely important to their effectiveness For the greatest success seek the advice of ashade tree professional experienced in laying out these lines Other factors which may affect thesuccess of root graft barriers are soil type tree size and spacing and the history of disease in the area(Note a map of barrier locations can be invaluable if follow-up work is necessary)

At first costs for oak wilt control may seem excessive But the alternative costs of doing nothing (lossof value of healthy trees dying from oak wilt property value decline tree removal and increasedheating and cooling costs) may be far more expensive Some contractors charge by the job by thefoot or by the hour All have a minimum charge to cover the cost of equipment insurance andtransportation Oak wilt control on a neighborhood or community level is strongly recommendedit can significantly decrease costs while increasing the effectiveness of control work

Persons hiring contractors to do oak wilt control work on their property should ask for referencesinquire about experience and be sure the contractor is insured

NO

NO

Do not trim or wound healthy oak trees during the springtime from April 15 to July 1If an oak is injured at this time of year cover wound immediately with a non-toxic treewound dressing

healthy red oaksthere other

nearby (within50 feet)

Are

die in July orAugust

Didthe trees

Figure 4 Flowchart - Oak wilt control in red oaks

These trees may produce oak wiltspores during the springtime (theonly time insect transmissionoccurs) These trees need to beremoved prior to April 15 of thefollowing year and covered with 4+mil plastic from April 15 to July 1This wood can be used

YES

Do not remove diseased treesright away This may acceleratethe movement of the fungus intosurrounding healthy oaks throughroot grafts

RED OAKS DIAGNOSED AS HAVING OAK WILT

Control measures may benecessary Sever common rootsystems with a vibratory plow ortrencher or boom (5 ft blade)or use chemical means to isolateroot systems of infected trees

YES

Unless these trees are in dangerof falling on people or propertythey can be removed whenconvenient and the wood used

OAK WILT CONTROL PROGRAMMINNESOTA DEPARTMENT OF AGRICULTURE

Plant Protection Division bull 625 Robert St N bull St Paul MN 55155-2538Telephone (651) 201-6020 Fax (651) 201-6108 Web wwwmdastatemnus

For more information contact Richard Hauer oak wilt program coordinator at the Minnesota Departmentof Agriculture Plant Protection Division This brochure was originally developed by David Stephenson withtechnical assistance from DW French professor of plant pathology at the University of Minnesota Figure3 used with permission of the University of Minnesota Extension Service Figure 1 courtesy of Ken HolmanAdditional copies of this publication or fact sheets on Organizing a Community Oak Wilt Control ProgramOak Wilt Control and Prevention on Construction Sites and Oak Wilt in Minnesota are available free ofcharge by writing to the address below The oak wilt control program in Minnesota is a multi-agency effort

involving the Department of Agriculture Department of Natural Resources Minnesota ExtensionService University of Minnesota USDA Forest Service and counties and communities across the

state

Rev 299 RJH

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

CONTROL DUTCH ELM DISEASE vs OAK WILT DUTCH ELM DISEASE OAK WILT Spread Over 90 is overland by beetles Over 90 is through root grafts

Control emphasis Bark beetle reduction Root graft disruption

ROOT TRANSMISSION AND CONTROL

When symptoms are first visible

The fungus is in the general area of the wilt symptoms (when infection is from beetles)

The fungus is throughout the tree and into the root system

Control 1 Immediate removal to prevent movement of fungus into roots Radical pruning if wilt is very isolated

2 If the infection is from root

transmission root graft disruption should be done first

Root graft disruption if healthy oaks (of the same species) are nearby Do not remove the tree first

AERIAL TRANSMISSION AND CONTROL

Beetle characteristics 1 Attracted specifically to elms 2 Can chew through bark 3 Can travel long distances 4 Active all summer 5 Breeds in dead or dying bark-intact

elm wood

1 Not attracted specifically to oaks

2 Can only enter a tree through fresh wounds

3 Does not travel very far

4 Active primarily in springtime

5 Does not breed in oak wood

Control Remove and dispose of all deaddying bark-intact elm wood This will remove the breeding sites of the beetle

1 Donrsquot prune in April May and June

2 Locate remove and dispose of diseased oaks producing spores in early spring (March and April)

Plant Protection Division 625 Robert St N St Paul MN 55155-2538 651-201-6020

Rev 299 RJH

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

JAN FEB APR MAY OCT DEC

JAN FEB APR MAY OCT DEC

SAFE period

JAN FEB APR MAY OCT NOV DEC

University of Minnesota- Forest Resources Extension amp Outreach 2007Adapted from Minnesota Department of Agriculture RJH 1999 version Oak wilt reviewer Jennifer Juzwik USDA Forest Service- Research Plant Pathologist

OAK WILT CONTROL TIMETABLEMAR JUNE JULY AUG SEPT NOV

Oak removal amp proper disposal

mid-Nov to March 31st

Oak removal amp proper disposal mid-Nov to March

31st

NOTE Spore mats in infected trees can be observed throughout the winter In order to prevent overland spread infected trees (shown to produce spore mats) need to be properly wrappeddisposed of by March 31st

Disease transmission through

wounding

MAR JUNE JULY

SAFE period HIGH risk period

Cover hazardous wood

SEPT

Field ID of diseased oaks

LOW risk period

AUG SEPT

High-risk elm ID

Low-risk elm ID

MAR JUNE JULY AUG

NOV

NOTE High-risk elms must be removed within approximately twenty days Low-risk should be removed within twenty days but no later than April 1 of the following year

Root graft disruption (until ground freezes)

DUTCH ELM DISEASE CONTROL TIMETABLE

3rd Insp

Root graft disruption (until ground freezes)

Inspection of healthy elms

Elm firewood ID amp disposal (Disposal of low-risk elms from

previous year by 41)

1st Insp 2nd Insp

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Emerald Ash Borer Jeffrey Hahn Assistant Extension Entomologist

Copyright copy 2009 Regents of the University of Minnesota All rights reserved

The emerald ash borer (EAB) Agrilius planipennis is a very destructive insect pest of ash trees (Fraxinus spp) the only known hosts of this borer in the United States This exotic borer is a native of Asia with its natural range including China Japan Mongolia Korea the Russian Far East and Taiwan

It was first discovered in North America in southeast Michigan in June 2002 although it was

likely introduced at least 10 years earlier It has since been found in the US states of Ohio (2003) Indiana (2004) Maryland (2006) Illinois (2006) Pennsylvania (2007) West Virginia (2007) Wisconsin (2008) Missouri (2008) and Virginia (2008) It has also been found in the Canadian provinces of Ontario (2002) and Quebec (2008) In May 2009 it was discovered in St Paul Minnesota

Why is this insect important This destructive beetle has killed tens of millions of ash trees where it has been discovered There are about 870 million ash trees in Minnesota one of the largest concentrations of ash of any state in the country Not only are these trees abundant in our forests but they are also an important component of our urban landscapes Research has not found any resistance in our native ash We could lose much of this resource

How Do I Recognize This Insect EAB is a slender elongate insect about 13 - 12 inch long It is widest just behind the head gradually tapering back to the abdomen It is a bright iridescent green to copper-green color often with a copper colored area behind the head Its body underneath the wings is a purplish-magenta color

Emerald Ash Borer - Jeff Hahn

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Emerald Ash Borer with wings open - Jeff Hahn Insects in Minnesota that may be confused with Emerald Ash Borer

This borer is a type of metallic wood boring beetle (family Buprestidae) and is closely related to the bronze birch borer and the twolined chestnut borer both native insects in Minnesota EAB however is a bit larger and much more brightly colored than these species

Not every green insect you see is an EAB There are several common insects that look similar especially the six-spotted tiger beetle and the polydrusus weevil A six-spotted tiger beetle is a similar size about 38 ndash 12 inch long but with a conspicuous large head and eyes It is also a different shape with the abdomen being wider than the head The polydrusus weevil is a small 14 inch long oval insect with a short snout It has a black body covered with pale metallic green scales

Also not every insect you find attacking ash is an EAB as there are many native ash borers present in Minnesota The most common are redheaded ash borer bark beetles and clearwing borers For more information see native borers and emerald ash borer look-alikes [PDF] (wwwmdastatemnusnewspublicationsexteablookalikespdf )

Biology Picture to left Emerald Ash Borer larvae - David Cappaert Michigan State University Bugwoodorg

EABs generally have a one year life cycle although that can be extended to two years in a vigorous host These insects overwinter as fully grown larvae in chambers constructed under the bark of ash trees They pupate in early spring and emerge as

adults leaving characteristic D-shaped emergence holes Depending on where you live in Minnesota expect adults to emerge any time from late May to August

After feeding on leaves adults mate and females lay eggs on the bark or in small cracks in it Eggs hatch in 7 to 10 days The whitish larvae called flatheaded borers tunnel under the bark creating a series of winding S-shaped galleries in the phloem and outer sapwood These tunnels girdle the trunk and branches interrupting the flow of water and nutrients The larvae feed until fall then overwinter as prepupal larvae

Symptoms and Damage Trees typically are killed in two to four years When trees are first attacked by EABs the symptoms are inconspicuous and hard to notice By the end of the second year thinning foliage and dieback in the crown begins to be apparent By the third year there is severe dieback and little foliage Ash can tolerate small numbers of EAB larvae but trees are girdled and killed when populations become more numerous

When the adults emerge they create small 18 inch D-shaped exit holes that are characteristic of this insect although they can be hard to see If you were to remove the bark on the trunk of a tree showing these symptoms you should also find the larval galleries Epicormic sprouts may form on the lower trunk and major branches as the tree responds to emerald ash borer activity Woodpecker attacks on ash could also indicate the presence of emerald ash borers Vertical splits in the bark due to callous tissue forming over old galleries may also be seen

All species of ash are attacked including all ash species found in Minnesota green (F pennsylvanica) black (F nigra) and white ash (F americana) Mountain ash (Sorbus spp) is not a true ash and is not attacked Emerald ash borer attacks ash of different sizes from as small as one inch diameter to large mature trees They commonly attack stressed and unhealthy trees first similar to the native bronze birch borer and twolined chestnut borer However unlike these insects EABs will also successfully attack vigorously growing trees Once an ash is attacked by EABs it will be killed

Keep in mind there are other problems that can cause an ash tree to decline Go to Whatrsquos Wrong With My Ash for help in diagnosing an ash problem (httpwwwextensionumnedugardeninfodiagnosticsdeciduousashindexhtml )

D-shaped exit holes - Jeff Hahn Emerald Ash Borer killed trees - Jeff Hahn

Emerald Ash Borer galleries - Jeff Hahn

Epicormic sprouts - Jeff Hahn

What Can I Do To Help First donrsquot transport firewood when you go camping or are buying it for home use even if it is within Minnesota Just buy the wood you need at local sites or at the campgrounds you are visiting On its own EAB will generally move only about 12 mile a year from infested sites But with help from people it can travel hundreds of miles when carried in firewood and other wood products or nursery stock Next be aware of what an EAB looks like as well as the symptoms of an EAB infested tree Report any suspect insects or declining ash trees (see ldquoWhat Can I Do If I Suspect I Have Found EABrdquo) There have been many cases where the public was the first to find an initial infestation in an area

What Can I Do If I Suspect I Have Found EAB First use the diagnostic page [PDF] (wwwmdastatemnusnewspublicationspestsplantspestmanagementeab_doihaveitpdf ) to see if you can clearly rule out EAB If after you have gone through this page you can not easily rule out EAB then you will be asked to contact the Forest Resources Extension and Outreach to find an EAB First Detector near you They will help you determine whether your situation needs to be examined more closely You can also contact the Minnesota Department of Agriculture on their Arrest the Pest Hotline at 651-201-6684 or 1-888-545-6684 to report your suspicions

Should I Be Planting or Removing Ash Because of the overabundance of ash in urban landscapes and other sites it is strongly recommended not to plant additional ash Consider the other woody plant options that are available to Minnesotans However if you have an ash in your yard and it is healthy there is no reason to remove it As long as it is a low maintenance plant keep it in your landscape

Should I Be Treating My Ash There are insecticides that are available to protect ash from EAB However as long as there isnrsquot a confirmed infestation in Minnesota the odds of any given tree becoming infested with EAB are very low

It is true that infestations in other states usually have gone undetected five years or more before they are discovered which might also be the case in Minnesota However EAB does not kill every tree in an area overnight University experts throughout the EAB-infested states do not advise insecticide treatments without a confirmed infestation within 12 to 15 miles

This advice is based on the probability of a tree becoming infested with emerald ash borer There will be enough time to decide whether or not to treat your trees once EAB is actually found in Minnesota Some of the chemicals used to protect trees from EAB can be highly effective but such treatments in the absence of a confirmed infestation are very likely to add years of unnecessary applications and expense

United States

Department of Agriculture

Forest Service

Northeastern Area State and Private Forestry

NAndashPRndash04ndash0

Figure 1 Forest tent caterpillar egg masses

Forest Tent Caterpillar The forest tent caterpillar (Malacosoma disstria Huumlbner) is a native insect found throughout the range of hardwood forests in North America It is more abundantly distributed in eastern North America but is also common in western areas that have large stands of aspen At times this insect can be a damaging defoliator of trees Trees that are defoliated often flush a new smaller set of leaves in July While forest tent caterpillar does not typically cause mortality to host trees mortality can occur when populations interact with other disturbances such as drought or insect outbreaks Forest tent caterpillar larvae use silk to form trails and to create pads on host trees where they congregate and rest However they do not construct and reside within elaborate silken tents A different species the eastern tent caterpillar forms these more defined tents in branch crotches of cherry and other trees in the rose family

Figure 2 Forest tent caterpillar larvae

Hosts Because forest tent caterpillar is found throughout much of North America it is no surprise that it has a large host range Depending on the geographic region ash aspens basswood birch cherry cottonwood elms oaks red alder sugar maple swamp blackgum sweetgun water tupelo and willow are all potential hosts Forest tent caterpillar does not feed on red maple sycamore or conifers

Figure 3 Forest tent caterpillar pupa in cocoon

Description Eggs are laid in dark masses (25ndash37 mm wide) that surround small twigs (figure 1) These masses may contain up to 350 eggs Newly hatched larvae are 3 mm in length black and have noticeable hairs As larvae grow and become a more brownish color two distinct characteristics develop Pale bluish lines form along the margins of the larvae and white spots (often described as footprints or keyholes) develop along the back (figure 2) Full-grown larvae are about 50 mm in length Pupae are protected by a cocoon spun from pale yellow silk and are often found in protected areas (figure 3) Adult moths are light brown with two narrow dark bands on the forewings and have a wingspan between 25 and 28 mm (figure 4)

Figure 4 Forest tent caterpillar adult moth

Life History Forest tent caterpillar populations usually cycle remaining high for 3 to 4 years before dropping to low levels due to harsh weather predation disease andor starvation Eggs hatch in the spring and larvae begin feeding on the newly expanded foliage of host trees During this time larvae can be seen following one another in straight lines and congregating Larvae feed into June and

then pupate in silken cocoons in protected areas or folded leaves Adults emerge in July locate hosts mate and lay eggs Egg masses are deposited around small twigs of host trees and are often concentrated on trees near well-lit urban areas The adult moths are nocturnal and are strongly attracted to light

Management Options Several options are available for managing forest tent caterpillar Because trees usually survive defoliation the first option to consider is doing nothing to manage the population Environmental conditions as well as natural predators help regulate forest tent caterpillar populations after only a few years If control is necessary mechanical and insecticidal options exist Mechanical options include placing barriers on trees removing egg masses before they hatch and removing larvae when they are congregated Insecticides such as Bacillus thuringiensis (Bt) can be used to protect weakened trees or to cover large areas where populations have remained high for consecutive years Management decisions can be guided by egg mass surveys For example an average of 20 or more egg masses over 15 cm in diameter per tree indicates the likelihood of complete defoliation and may necessitate a management response

Pesticide Precautionary Statement

Pesticides used improperly can be injurious to humans animals and plants Follow the directions and heed all precautions on the labels Note Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

Authors Kevin J Dodds USDA Forest Service Northeastern Area State and Private Forestry Forest Health Protection Durham NH Steven J Seybold USDA Forest Service Pacific Southwest Research Station Davis CA

Photo credits Ronald S Kelley Forest Insect and Disease Specialist Vermont Department of Forests Parks and Recreation Morrisville VT

For more information contact the office nearest you

USDA Forest Service Forest Health Protection 271 Mast Road Durham NH 03824 6038687600

USDA Forest Service Forest Health Protection 1992 Folwell Avenue St Paul MN 55108 6516495243

USDA Forest Service Forest Health Protection 180 Canfield Street Morgantown WV 26505 3042851542

USDA Forest Service Forest Health Protection 1720 Peachtree Road NW Rm 862N Atlanta GA 30367 4043472961

USDA Forest Service Northeastern Area State and Private Forestry Newtown Square PA The USDA is an equal opportunity

provider and employer httpwwwnafsfedus

then pupate in silken cocoons in protected areas or folded leaves Adults emerge in July locate hosts mate and lay eggs Egg masses are deposited around small twigs of host trees and are often concentrated on trees near well-lit urban areas The adult moths are nocturnal and are strongly attracted to light

Management Options Several options are available for managing forest tent caterpillar Because trees usually survive defoliation the first option to consider is doing nothing to manage the population Environmental conditions as well as natural predators help regulate forest tent caterpillar populations after only a few years If control is necessary mechanical and insecticidal options exist Mechanical options include placing barriers on trees removing egg masses before they hatch and removing larvae when they are congregated Insecticides such as Bacillus thuringiensis (Bt) can be used to protect weakened trees or to cover large areas where populations have remained high for consecutive years Management decisions can be guided by egg mass surveys For example an average of 20 or more egg masses over 15 cm in diameter per tree indicates the likelihood of complete defoliation and may necessitate a management response

Pesticide Precautionary Statement

Pesticides used improperly can be injurious to humans animals and plants Follow the directions and heed all precautions on the labels Note Some States have restrictions on the use of certain pesticides Check your State and local regulations Also because registrations of pesticides are under constant review by the Federal Environmental Protection Agency consult your county agricultural agent or State extension specialist to be sure the intended use is still registered

Authors Kevin J Dodds USDA Forest Service Northeastern Area State and Private Forestry Forest Health Protection Durham NH Steven J Seybold USDA Forest Service Pacific Southwest Research Station Davis CA

Photo credits Ronald S Kelley Forest Insect and Disease Specialist Vermont Department of Forests Parks and Recreation Morrisville VT

For more information contact the office nearest you

USDA Forest Service Forest Health Protection 271 Mast Road Durham NH 03824 6038687600

USDA Forest Service Forest Health Protection 1992 Folwell Avenue St Paul MN 55108 6516495243

USDA Forest Service Forest Health Protection 180 Canfield Street Morgantown WV 26505 3042851542

USDA Forest Service Forest Health Protection 1720 Peachtree Road NW Rm 862N Atlanta GA 30367 4043472961

USDA Forest Service Northeastern Area State and Private Forestry Newtown Square PA The USDA is an equal opportunity

provider and employer httpwwwnafsfedus

United States Department of Agriculture

Forest Service Northeastern Area

State and Private Forestry NAndashPRndash02ndash11

May 2011

Bur Oak Blight A serious leaf blight disease on bur oak has been recognized in several Midwestern States since the 1990s with Iowa reporting its first occurrence of this disease 6 or 7 years ago A common leafspot fungus Tubakia dryina was initially thought to be the cause of the blight on bur oak but closer examination revealed a different story Researchers in Iowa confirmed that this disease is caused by a new and yet unnamed species of Tubakia The disease was named bur oak blight or BOB for short

There are now five known species of Tubakia that can infect bur oak in Iowa but only one species causes dramatic leaf symptoms and tree mortality characteristic of BOB

Hosts and Distribution BOB occurs only on bur oaks Severe symptoms of BOB have been observed only on Quercus macrocarpa var oliviformis a variety of bur oak that produces smaller acorns BOB occurs primarily on naturally established trees and especially on mature trees on upland sites that appear to be remnants of savannah forests Bur oak growing in dense forests and on bottomland sites is less seriously affected

It is not clear if this new species of Tubakia is a recent arrival to this region or if a shift in climate (more early-season rain events) has made this disease more noticeable over the last two decades To date the BOB fungus is known to occur from northeastern Kansas and eastern Nebraska to central Minnesota and southwestern Wisconsin and across most of Iowa This disease is most severe in eastern Nebraska Iowa and Minnesota which coincides closely with the distribution of Quercus macrocarpa var oliviformis A few affected trees have also been identified in Illinois and Missouri

Symptoms Leaf symptoms typically first appear in late July or August Infected leaves develop purple-brown lesions along the midvein and major lateral veins on the underside of leaves (figure 1) As the lesions increase in size dark veins become noticeable on the upper leaf surface (figure 2) Large wedge-shaped areas of chlorosis and necrosis develop on the leaf blade and major leaf mortality may occur (figure 2) Individual lesions may coalesce and cause large areas of the leaf to die giving it an overall wilted or scorched appearance (figure 3) The symptoms of wilting and leaf scorch resemble and have been confused with symptoms induced by oak wilt

During the summer black fruiting structures of the fungus form along the dark leaf veins and produce rain-splashed spores These fruiting bodies can be seen with the aid of a

10X magnifying lens (figure 4) Later in the season black pustules (fruiting bodies of the fungus) develop on the petioles of infected leaves (figure 5) and mature spores are seen in these pustules the next spring

A unique feature of BOB is that some of the killed leaves remain on the tree during the winter (healthy bur oak trees shed all of their leaves in the fall) Not all infected leaves however remain attached Some leaves drop off during the growing season and some are blown off by winter winds (figure 6) If BOB-infected leaves drop or are blown off their petioles typically remain attached to the tree The disease can be confirmed by microscopic examination of the pustules that form on the petiole base

The disease tends to intensify from year to year in individual trees If only a portion of the crown is affected BOB symptoms usually start in the lower branches and progress up the tree If a tree is seriously affected one year it tends to be severely affected the next year BOB appears to spread slowly particularly from tree to tree It remains a mystery why BOB does not spread more rapidly given the great abundance of spores that cause BOB and their spread by rain

Figure 1mdashPurple-brown lesions develop along the veins on the underside of leaves

Figure 2mdashDark veins and large wedge-shaped lesions develop

Figure 3mdashLarge areas of the leaf may die resulting in an overall wilted or scorched appearance

Figure 4mdashBlack fruiting bodies form on dark leaf veins (lower right) Rain-splashed spores are produced under a protective hyphal shield (upper right magnified 200X)

Figure 5mdashBlack pustules develop on infected leaf petioles

Figure 6mdash Many dead leaves remain on the tree throughout the winter

Figure 7mdash Affected trees typically occur next to unaffected trees

Not all stands of bur oak are seriously affected by this disease Even within a seriously affected stand not all trees are equally susceptible Some trees may be severely infected while adjacent trees appear healthy (figure 7) This is likely due to variation in the resistance of individual bur oak trees to this disease

Management Over time severely affected trees may die Tree death is usually associated with severe blight over many years and damage caused by secondary invaders such as the two-lined chestnut borer and Armillaria root rot Boosting tree vigor may prolong the life of affected trees and ward off invasion by secondary pests Because the fungus overwinters on infected leaf petioles that remain on the tree removing fallen leaves is not an effective management tool

In preliminary studies injections of the fungicide propiconazole (Alamo formulation) in late May or early June (prior to leaf symptoms) have reduced symptom development in the fall and the following year With further study fungicide treatments may have value in managing high-value landscape trees

Sample Submission When collecting samples for BOB testing collect branch twigs with symptomatic and healthy leaves as well as petioles from several locations on the tree and wrap them in dry paper toweling (no plastic bags please)

Submit samples to the National Plant Diagnostic Network (NPDN) Clinic in your respective State To find a clinic near you go to httpwwwnpdnorg

Contact information for authors

Jill D Pokorny Plant Pathologist US Forest Service Northeastern Area State and Private Forestry Forest Health Protection 1992 Folwell Ave Saint Paul MN 55108 651ndash649ndash5247

Dr Thomas C Harrington Iowa State University Department of Plant Pathology 221 Bessey Hall Ames IA 50011

Photo credits

Dr Thomas C Harrington Iowa State University Jill D Pokorny and Joseph G OrsquoBrien US Forest Service

Published by The USDA is an equal opportunity provider and employer USDA Forest Service Northeastern Area

Federal Recycling Program State and Private Forestry Printed on recycled paper 11 Campus Boulevard

Newtown Square PA 19073 wwwnafsfedus

Figure 3mdashLarge areas of the leaf may die resulting in an overall wilted or scorched appearance

Figure 4mdashBlack fruiting bodies form on dark leaf veins (lower right) Rain-splashed spores are produced under a protective hyphal shield (upper right magnified 200X)

Figure 5mdashBlack pustules develop on infected leaf petioles

Figure 6mdash Many dead leaves remain on the tree throughout the winter

Figure 7mdash Affected trees typically occur next to unaffected trees

Not all stands of bur oak are seriously affected by this disease Even within a seriously affected stand not all trees are equally susceptible Some trees may be severely infected while adjacent trees appear healthy (figure 7) This is likely due to variation in the resistance of individual bur oak trees to this disease

Management Over time severely affected trees may die Tree death is usually associated with severe blight over many years and damage caused by secondary invaders such as the two-lined chestnut borer and Armillaria root rot Boosting tree vigor may prolong the life of affected trees and ward off invasion by secondary pests Because the fungus overwinters on infected leaf petioles that remain on the tree removing fallen leaves is not an effective management tool

In preliminary studies injections of the fungicide propiconazole (Alamo formulation) in late May or early June (prior to leaf symptoms) have reduced symptom development in the fall and the following year With further study fungicide treatments may have value in managing high-value landscape trees

Sample Submission When collecting samples for BOB testing collect branch twigs with symptomatic and healthy leaves as well as petioles from several locations on the tree and wrap them in dry paper toweling (no plastic bags please)

Submit samples to the National Plant Diagnostic Network (NPDN) Clinic in your respective State To find a clinic near you go to httpwwwnpdnorg

Contact information for authors

Jill D Pokorny Plant Pathologist US Forest Service Northeastern Area State and Private Forestry Forest Health Protection 1992 Folwell Ave Saint Paul MN 55108 651ndash649ndash5247

Dr Thomas C Harrington Iowa State University Department of Plant Pathology 221 Bessey Hall Ames IA 50011

Photo credits

Dr Thomas C Harrington Iowa State University Jill D Pokorny and Joseph G OrsquoBrien US Forest Service

Published by The USDA is an equal opportunity provider and employer USDA Forest Service Northeastern Area

Federal Recycling Program State and Private Forestry Printed on recycled paper 11 Campus Boulevard

Newtown Square PA 19073 wwwnafsfedus

US Department of the Interior US Geological Survey

Great Lakes Science Center 1451 Green Road Ann Arbor MI 48105 (734) 994-3331 wwwglscusgsgov

GLSC Fact Sheet 2007-2

American and Oriental Bittersweet Identification

I nvasive species are one of the greatest threats to native ecosystems They can crowd out native species and

change the natural nutrient cycling processes that take place in ecosystems

One of the best ways to combat invasive species is by identifying small infestations and removing them

One invader threatening midwestern ecosystems is oriental bittersweet (Celastrus orbiculatus) This woody vine was introduced to the eastern United States in the mid-1800s It has spread from the east to the south and west and is now moving into midwestern natural areas Oriental bittersweet can be found in a variety of habitats from roadsides to interior forests and sand dunes It has the ability to girdle and overtop adjacent vegetation ndash often to the detriment of native species To halt the spread of oriental bittersweet significant control measures are needed

However a native bittersweet species American bittersweet (Celastrus scandens) can be mistaken for oriental bittersweet Although American bittersweet is also a

vine and climbs on nearby vegetation it does not appear to grow as rapidly or as large as oriental bittersweet In the northeastern United States American bittersweet is declining because of habitat change and possible hybridization while in the Midwest it is still common

Because the two bittersweet species look so similar there can be difficulty knowing

which plants to target for control Using fruit and leaf characters the two species can be discriminated from each other However certain traits are more reliable for correct identification than others Classically the position of the fruit and flowers on the stems has been cited as the most definitive means of discriminating between the species

Oriental bittersweet has fruit and flowers located in the leaf axils along the length of the stem American bittersweet however only has fruit and flowers in terminal clusters There is also a difference in the color of the capsules surrounding the ripened fruit in the fall Oriental bittersweet has yellow capsules while those of American bittersweet are orange Another difference in color is the pollen color of the male flowers The pollen of oriental bittersweet is white while that of American bittersweet is yellow

Some less definitive fruit traits for discrimination are size of the fruits and number of seeds per fruit American bittersweet has generally larger fruit than oriental bittersweet If fruits have a volume of greater than 250 mm3 there is a 90 probability of a plant being American bittersweet while if the fruit has a volume of 115 mm3 or less it has a 90 chance of being oriental bittersweet Values in between these numbers overlap to some extent between the species Similarly if the fruit has one or fewer seeds it is 90 likely to be American bittersweet while five or more seeds have a 90 chance of being oriental bittersweet The greater number of seeds of oriental bittersweet gives it a reproductive advantage over the native species The problem with using fruit and flower traits for discriminating between the two species is that for fruits only mature

female plants have this character available for identification In terms of flowers only mature male and female plants have these present and only for a brief time of the year during the spring

Vegetative traits apply to plants regardless of their sex or maturity The most definitive vegetative trait is the posture of the leaves at leaf out of the first buds in the spring The leaves of oriental bittersweet are conduplicate (two sides of the leaf folded against each other) and tightly packed in the bud when they emerge in the spring The leaves of American bittersweet are involute (leaf margins rolled in like a scroll) and not as tightly packed in the bud

Other leaf traits are not as reliable as the leaf-out posture Although the ratio of length-to-width (lengthwidth) of the leaves is generally greater for American bittersweet this trait is quite variable If the lengthwidth of the leaf is greater than or equal to 2 there is a 90 chance of the plant being American bittersweet while if the ratio is less than or equal to 14 there is a 90 chance of it being oriental bittersweet The tips of the leaves of American bittersweet are also generally longer than those of oriental bittersweet Plants with leaf tips of 15 cm or greater have a 90 chance of being American bittersweet while plants with leaf tips of 03 cm or less have a 90 chance of being oriental bittersweet

By using these traits plants could be marked at the appropriate time of year (spring or fall) for control at a later point In this manner the invasive species can be targeted without harming the native The key on the next page summarizes the key traits for discrimination of these two species in the field

Oriental bittersweet

American bittersweet

yellow

orangeYesIs plant in fruit Are ripe fruit capsules yellow

C scandensC orbiculatus

Are fruit borne in

Do fruits have le one seed

ge five seeds

C scandens

C orbiculatus

No

Is plant in bloom Yes Are flowers borne in terminal panicles

axillary cymes

C scandens

C orbiculatus

Are flowers staminate Yes

No

Is plant leafing out Are leavesYes

No

C scandens

C orbiculatusIs lengthwidth le 14

Are mature leaves present Is lengthwidth ge 20Yes

C scandens

C orbiculatusIs leaf tip lt 03 cm

Is leaf tip gt 15 cmNo

If dormant season only fruit characters applicable

involute conduplicate

C scandens C orbiculatus

terminal panicles axillary cymes

C scandens C orbiculatus

Is pollen

white

C orbiculatusC scandens

Indicates a 90 probability of correct identification based on the data collected for this studyColors in text boxes are to be used as a guide only actual colors seen in the field may differ

Collaborators Noel B Pavlovic Stacey Leicht Young Ralph Grundel and Krystalynn J Frohnapple

Thousand Cankers Disease

United StatesDepartment of Agriculture

Forest ServiceNortheastern Area

State and Private ForestryNAndashPRndash02ndash10

October 2011 (revised)

Dieback and mortality of eastern black walnut (Juglans nigra) in several Western States have become more common and severe during the last decade A tiny bark beetle is creating numerous galleries beneath the bark of affected branches resulting in fungal infection and canker formation The large numbers of cankers associated with dead branches suggest the diseasersquos namemdashthousand cankers disease

The principal agents involved in this disease are a newly identified fungus (Geosmithia sp with a proposed name of Geosmithia morbida) and the walnut twig beetle (Pityophthorus juglandis) Both the fungus and the beetle only occur on walnut species An infested tree usually dies within 3 years of initial symptoms

Thousand cankers disease has been found in many Western States (figure 1) The fungus and the beetle have not been found east of the Great Plains However a number of factors suggest that this disease could establish in eastern forests the widespread distribution of eastern black walnut the susceptibility of this tree species to the disease and the capacity of the fungus and beetle to invade new areas and survive under a wide range of climatic conditions in the West

Disease SymptomsThe three major symptoms of this disease are branch mortality numerous small cankers on branches and the bole and evidence of tiny bark beetles The earliest symptom is yellowing foliage that progresses rapidly to brown wilted foliage then finally branch mortality (figure 2) The fungus causes distinctive circular to oblong cankers in the phloem under the bark which eventually kill the cambium (figure 3) The bark surface may have no symptoms or a dark amber stain or cracking of the bark may occur directly above a canker Numerous tiny bark beetle entrance and exit holes are visible on dead and dying branches (figure 4) and bark beetle galleries are often found within the cankers In the final stages of disease even the main stem has beetle attacks and cankers

Geosmithia spMembers of the genus Geosmithia have not been considered to be important plant pathogens but Geosmithia morbida appears to be more virulent than

Figure 1 Thousand cankers disease occurs in 9 western states the year in which the disease was confirmed is noted Since 2010 TCD has been found in three locations in the East (TN VA PA - see ) The native ranges of eastern black walnut (dark green) and four western black walnut species (light green) are shown Eastern black walnut is widely planted in the West but is not depicted on this map

Figure 2 Wilting black walnut in the last stages of thousand cankers disease

Figure 3 Small branch cankers caused by Geosmithia morbida

Published by USDA Forest Service Northeastern Area State and Private Forestry 11 Campus Boulevard Newtown Square PA 19073 wwwnafsfedus

Federal Recycling ProgramPrinted on recycled paper

USDA is an equal opportunity provider and employer

related species Aside from causing cankers the fungus is inconspicuous Culturing on agar media is required to confirm its identity Adult bark beetles carry fungal spores that are then introduced into the phloem when they construct galleries Small cankers develop around the galleries these cankers may enlarge and coalesce to completely girdle the branch Trees die as a result of these canker infections at each of the thousands of beetle attack sites

Walnut Twig BeetleThe walnut twig beetle is native to Arizona California and New Mexico It has invaded Colorado Idaho Oregon Utah and Washington where walnuts have been widely planted The beetle has not caused significant branch mortality by itself Through its association with this newly identified fungus it appears to have greatly increased in abundance Adult beetles are very small (15 to 20 mm long or about 116 in) and are reddish brown in color (figure 5) This species is a typical-looking bark beetle that is characterized by its very small size and four to six concentric ridges on the upper surface of the pronotum (the shield-like cover behind and over the head) (figure 5A) Like most bark beetles the larvae are white C shaped and found in the phloem For this species the egg galleries created by the adults are horizontal (across the grain) and the larval galleries tend to be vertical (along the grain) (figure 6)

Survey and SamplesVisually inspecting walnut trees for dieback is currently the best survey tool for the Eastern United States Look for declining trees with the symptoms described above If you suspect that your walnut trees have thousand cankers disease collect a branch 2 to 4 inches

Figure 4 Exit holes made by adult walnut twig beetles

in diameter and 6 to 12 inches long that has visible symptoms Please submit branch samples to your Statersquos plant diagnostic clinic Each State has a clinic that is part of the National Plant Diagnostic Network (NPDN) They can be found at the NPDN Web site (wwwnpdnorg) You may also contact your State Department of Agriculture State Forester or Cooperative Extension Office for assistance

Prepared by Steven Seybold Research Entomologist US Forest Service Pacific Southwest Research StationDennis Haugen Forest Entomologist and Joseph OrsquoBrien Plant Pathologist US Forest Service Northeastern Area State and Private ForestryAndrew Graves Postdoctoral Research Associate UC-Davis Department of Plant Pathology

Photographs Figure 1 Andrew GravesFigure 2 Manfred Mielke US Forest Service Figures 3 4 6 Whitney Cranshaw Colorado State University wwwforestryimagesorg Figure 5 Steve Valley Oregon Department of Agriculture

Figure 6 Walnut twig beetle galleries under the bark of a large branch

Figure 5 Walnut twig beetle top view (A) and side view (B)

18 mm

A

B

Websites to study and look through Click on link address to view publication

How to Manage DED

httpwwwnafsfedusspfopubshowtosht_dedht_dedhtm

Oak Wilt in Minnesota

httpwwwextensionumnedudistributionnaturalresourcesDD3174html

Forest Tent Caterpillar

httpwwwnafsfedusspfopubspest_alftcftchtm

Gypsy moth information

httpwwwmdastatemnusplantspestmanagementgmunitgmhistoryaspx

Gypsy Moth Life Cycle

httpwwwmdastatemnusenplantspestmanagementgmunitgmbiologyaspx

Save our Ash

httpwwwmdastatemnusplantspestmanagementeabaspx

Signs and Symptoms of the Emerald Ash Borer httpwwwtwpindependencemiusServicesPublicWorksEnvironmentalNewsE2938pdf

Whatrsquos In That Wood Pile

httpwwwagdepartmentcomProgramsppEABFilesWhatsInThatWoodPilepdf

Practice Tree Inspector Certification Exam Answers to these questions can be found in readings in the study packet

These practice questions will give you an idea on the types of topics level of difficulty and format of questions to expect in the exam

1 Firewood restrictions are in place to reduce the spread of a Ash plant bug b Emerald ash borer c Ash flower gall d Ash rust

2 ldquoAvoidedrdquo food of a gypsy moth includes a beech buckeye hornbeam maple b ash catalpa dogwood locust c spruce pine larch d aspen oak poplar willow

3 Gypsy moths are established in Minnesota

a True b False

4 Signs of emerald ash borer attack on standing trees or firewood logs include a O-shaped exit holes b D-shaped exit holes c S-shaped galleries in the sapwood under the bark d Y-shaped galleries in the sapwood under the bark e A and D f B and C

5 Forest tent caterpillars prefer to feed on the following group of trees a Elms oaks pine species b Ash cherry spruce species c Red maple and sycamore d Basswood birch sugar maple

6 The forest tent caterpillar damage does not usually cause mortality in trees but if management is desired it should include one of the following management strategies

a Pyridaben applications b Bifenthrin applications c Bacillus thuringiensis applications d Dicofol applications

7 Oak wilt can be spread by root grafts and a Insects chewing into bark b Insects attracted to fresh pruning wounds c Spores carried by wind d Spores carried by rain

8 Oak wilt is a disease caused by the pathogen a Ceratosystis fagacearum b Ophiostpma ulmi c oak bark beetle d oak leaf beetle

9 A red oak tree that is infected will generally completely wilt within this time frame a 1 week b 1-2 weeks c 2-6 weeks d 4-8 weeks

10 What is the percentage of oak wilt disease spread through root grafts a 10 b 30 c 60 d 90

11 If you identify a red oak tree with oak wilt that has several uninfected red oaks surrounding it you should first a Remove the infected tree as soon as possible b Prune the uninfected red oaks before they become infected c Trench around the infected tree d Prune the infected red oak before it spreads it to the others

12 A year is divided into three distinct categories for oak pruning and the overland spread of oak wilt by beetles- high risk

low risk and safe period The ldquolow risk periodrdquo is associated with a November December January b January February March c April May June d July August September October

13 Which of the following trees can be identified by the distinct alternating bands of light and dark colored bark a American elm and rock elm b Siberian elm c Red elm and rock elm d All of the above

14 How many times during the growing season should a Tree inspector check for Dutch elm disease symptoms on elm trees a At least once b At least twice c At least three times d At least four times

15 Sapwood staining or discoloration is a common symptom of Dutch elm disease a True b False

16 Dutch elm disease can be found on a American and Siberian elm b Rock and red elm c Red and American elm d All of the above

17 Dutch elm disease can be spread by root grafts and a Insects chewing through the bark of young branch unions b Insects transported by wood chips from diseased elm trees c Spores carried by wind d Spores carried by rain

18 Native elm bark beetles normally have _____ generation(s) in one year in Minnesota a 1 b 2 c 3 d 4

19 European elm bark beetles overwinter as a Adults b Pupae c Juveniles d Larvae

20 All dead and dying elm trees from the previous year must be removed and properly disposed or treated prior to April 1st a True b False

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

• complete with cover for digital copy
• • ti study packet web cover 2012
  • ti study packet complete less cover
  • • ti study packet contents 2012
    • IdentifyandManageDutchElmDisease
    • DEDmanagement
    • DEDfuture
    • OakWiltinMinnesota
    • OW root graft control barriers
    • Control DEDvsOW
    • OWDEDTimetable
    • EmeraldAshBorer Jeff Hahn
    • ForestTentCaterpillar PEST ALERT
    • BUR OAK BLIGHT PEST ALERT
    • Amer and otiental bittersweet id USGS
    • • Invasive species are one of the greatest threats to native ecosystems They can crowd out native species and change the natural nutrient cycling processes that take place in ecosystems13
      • • thousand_cankers_disease_print_res
        • Web Sites3
        • • studyExamFinal
          • studyExamAnswers

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 DEU 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 ESP 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 FRA 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 ITA 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 JPN ltFEFF9ad854c18cea306a30d730ea30d730ec30b951fa529b7528002000410064006f0062006500200050004400460020658766f8306e4f5c6210306b4f7f75283057307e305930023053306e8a2d5b9a30674f5c62103055308c305f0020005000440046002030d530a130a430eb306f3001004100630072006f0062006100740020304a30883073002000410064006f00620065002000520065006100640065007200200035002e003000204ee5964d3067958b304f30533068304c3067304d307e305930023053306e8a2d5b9a306b306f30d530a930f330c8306e57cb30818fbc307f304c5fc59808306730593002gt13 KOR ltFEFFc7740020c124c815c7440020c0acc6a9d558c5ec0020ace0d488c9c80020c2dcd5d80020c778c1c4c5d00020ac00c7a50020c801d569d55c002000410064006f0062006500200050004400460020bb38c11cb97c0020c791c131d569b2c8b2e4002e0020c774b807ac8c0020c791c131b41c00200050004400460020bb38c11cb2940020004100630072006f0062006100740020bc0f002000410064006f00620065002000520065006100640065007200200035002e00300020c774c0c1c5d0c11c0020c5f40020c2180020c788c2b5b2c8b2e4002egt13 NLD (Gebruik deze instellingen om Adobe PDF-documenten te maken die 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 SUO 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 SVE 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 ENU (Use these settings to create Adobe PDF documents best suited for high-quality prepress printing Created PDF documents can be opened with Acrobat and Adobe Reader 50 and later)13 gtgt13 Namespace 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yellow

orangeYesIs plant in fruit Are ripe fruit capsules yellow

C scandensC orbiculatus

Are fruit borne in

Do fruits have le one seed

ge five seeds

C scandens

C orbiculatus

No

Is plant in bloom Yes Are flowers borne in terminal panicles

axillary cymes

C scandens

C orbiculatus

Are flowers staminate Yes

No

Is plant leafing out Are leavesYes

No

C scandens

C orbiculatusIs lengthwidth le 14

Are mature leaves present Is lengthwidth ge 20Yes

C scandens

C orbiculatusIs leaf tip lt 03 cm

Is leaf tip gt 15 cmNo

If dormant season only fruit characters applicable

involute conduplicate

C scandens C orbiculatus

terminal panicles axillary cymes

C scandens C orbiculatus

Is pollen

white

C orbiculatusC scandens

Indicates a 90 probability of correct identification based on the data collected for this studyColors in text boxes are to be used as a guide only actual colors seen in the field may differ

Collaborators Noel B Pavlovic Stacey Leicht Young Ralph Grundel and Krystalynn J Frohnapple

Thousand Cankers Disease

United StatesDepartment of Agriculture

Forest ServiceNortheastern Area

State and Private ForestryNAndashPRndash02ndash10

October 2011 (revised)

Dieback and mortality of eastern black walnut (Juglans nigra) in several Western States have become more common and severe during the last decade A tiny bark beetle is creating numerous galleries beneath the bark of affected branches resulting in fungal infection and canker formation The large numbers of cankers associated with dead branches suggest the diseasersquos namemdashthousand cankers disease

The principal agents involved in this disease are a newly identified fungus (Geosmithia sp with a proposed name of Geosmithia morbida) and the walnut twig beetle (Pityophthorus juglandis) Both the fungus and the beetle only occur on walnut species An infested tree usually dies within 3 years of initial symptoms

Thousand cankers disease has been found in many Western States (figure 1) The fungus and the beetle have not been found east of the Great Plains However a number of factors suggest that this disease could establish in eastern forests the widespread distribution of eastern black walnut the susceptibility of this tree species to the disease and the capacity of the fungus and beetle to invade new areas and survive under a wide range of climatic conditions in the West

Disease SymptomsThe three major symptoms of this disease are branch mortality numerous small cankers on branches and the bole and evidence of tiny bark beetles The earliest symptom is yellowing foliage that progresses rapidly to brown wilted foliage then finally branch mortality (figure 2) The fungus causes distinctive circular to oblong cankers in the phloem under the bark which eventually kill the cambium (figure 3) The bark surface may have no symptoms or a dark amber stain or cracking of the bark may occur directly above a canker Numerous tiny bark beetle entrance and exit holes are visible on dead and dying branches (figure 4) and bark beetle galleries are often found within the cankers In the final stages of disease even the main stem has beetle attacks and cankers

Geosmithia spMembers of the genus Geosmithia have not been considered to be important plant pathogens but Geosmithia morbida appears to be more virulent than

Figure 1 Thousand cankers disease occurs in 9 western states the year in which the disease was confirmed is noted Since 2010 TCD has been found in three locations in the East (TN VA PA - see ) The native ranges of eastern black walnut (dark green) and four western black walnut species (light green) are shown Eastern black walnut is widely planted in the West but is not depicted on this map

Figure 2 Wilting black walnut in the last stages of thousand cankers disease

Figure 3 Small branch cankers caused by Geosmithia morbida

Published by USDA Forest Service Northeastern Area State and Private Forestry 11 Campus Boulevard Newtown Square PA 19073 wwwnafsfedus

Federal Recycling ProgramPrinted on recycled paper

USDA is an equal opportunity provider and employer

related species Aside from causing cankers the fungus is inconspicuous Culturing on agar media is required to confirm its identity Adult bark beetles carry fungal spores that are then introduced into the phloem when they construct galleries Small cankers develop around the galleries these cankers may enlarge and coalesce to completely girdle the branch Trees die as a result of these canker infections at each of the thousands of beetle attack sites

Walnut Twig BeetleThe walnut twig beetle is native to Arizona California and New Mexico It has invaded Colorado Idaho Oregon Utah and Washington where walnuts have been widely planted The beetle has not caused significant branch mortality by itself Through its association with this newly identified fungus it appears to have greatly increased in abundance Adult beetles are very small (15 to 20 mm long or about 116 in) and are reddish brown in color (figure 5) This species is a typical-looking bark beetle that is characterized by its very small size and four to six concentric ridges on the upper surface of the pronotum (the shield-like cover behind and over the head) (figure 5A) Like most bark beetles the larvae are white C shaped and found in the phloem For this species the egg galleries created by the adults are horizontal (across the grain) and the larval galleries tend to be vertical (along the grain) (figure 6)

Survey and SamplesVisually inspecting walnut trees for dieback is currently the best survey tool for the Eastern United States Look for declining trees with the symptoms described above If you suspect that your walnut trees have thousand cankers disease collect a branch 2 to 4 inches

Figure 4 Exit holes made by adult walnut twig beetles

in diameter and 6 to 12 inches long that has visible symptoms Please submit branch samples to your Statersquos plant diagnostic clinic Each State has a clinic that is part of the National Plant Diagnostic Network (NPDN) They can be found at the NPDN Web site (wwwnpdnorg) You may also contact your State Department of Agriculture State Forester or Cooperative Extension Office for assistance

Prepared by Steven Seybold Research Entomologist US Forest Service Pacific Southwest Research StationDennis Haugen Forest Entomologist and Joseph OrsquoBrien Plant Pathologist US Forest Service Northeastern Area State and Private ForestryAndrew Graves Postdoctoral Research Associate UC-Davis Department of Plant Pathology

Photographs Figure 1 Andrew GravesFigure 2 Manfred Mielke US Forest Service Figures 3 4 6 Whitney Cranshaw Colorado State University wwwforestryimagesorg Figure 5 Steve Valley Oregon Department of Agriculture

Figure 6 Walnut twig beetle galleries under the bark of a large branch

Figure 5 Walnut twig beetle top view (A) and side view (B)

18 mm

A

B

Websites to study and look through Click on link address to view publication

How to Manage DED

httpwwwnafsfedusspfopubshowtosht_dedht_dedhtm

Oak Wilt in Minnesota

httpwwwextensionumnedudistributionnaturalresourcesDD3174html

Forest Tent Caterpillar

httpwwwnafsfedusspfopubspest_alftcftchtm

Gypsy moth information

httpwwwmdastatemnusplantspestmanagementgmunitgmhistoryaspx

Gypsy Moth Life Cycle

httpwwwmdastatemnusenplantspestmanagementgmunitgmbiologyaspx

Save our Ash

httpwwwmdastatemnusplantspestmanagementeabaspx

Signs and Symptoms of the Emerald Ash Borer httpwwwtwpindependencemiusServicesPublicWorksEnvironmentalNewsE2938pdf

Whatrsquos In That Wood Pile

httpwwwagdepartmentcomProgramsppEABFilesWhatsInThatWoodPilepdf

Practice Tree Inspector Certification Exam Answers to these questions can be found in readings in the study packet

These practice questions will give you an idea on the types of topics level of difficulty and format of questions to expect in the exam

1 Firewood restrictions are in place to reduce the spread of a Ash plant bug b Emerald ash borer c Ash flower gall d Ash rust

2 ldquoAvoidedrdquo food of a gypsy moth includes a beech buckeye hornbeam maple b ash catalpa dogwood locust c spruce pine larch d aspen oak poplar willow

3 Gypsy moths are established in Minnesota

a True b False

4 Signs of emerald ash borer attack on standing trees or firewood logs include a O-shaped exit holes b D-shaped exit holes c S-shaped galleries in the sapwood under the bark d Y-shaped galleries in the sapwood under the bark e A and D f B and C

5 Forest tent caterpillars prefer to feed on the following group of trees a Elms oaks pine species b Ash cherry spruce species c Red maple and sycamore d Basswood birch sugar maple

6 The forest tent caterpillar damage does not usually cause mortality in trees but if management is desired it should include one of the following management strategies

a Pyridaben applications b Bifenthrin applications c Bacillus thuringiensis applications d Dicofol applications

7 Oak wilt can be spread by root grafts and a Insects chewing into bark b Insects attracted to fresh pruning wounds c Spores carried by wind d Spores carried by rain

8 Oak wilt is a disease caused by the pathogen a Ceratosystis fagacearum b Ophiostpma ulmi c oak bark beetle d oak leaf beetle

9 A red oak tree that is infected will generally completely wilt within this time frame a 1 week b 1-2 weeks c 2-6 weeks d 4-8 weeks

10 What is the percentage of oak wilt disease spread through root grafts a 10 b 30 c 60 d 90

11 If you identify a red oak tree with oak wilt that has several uninfected red oaks surrounding it you should first a Remove the infected tree as soon as possible b Prune the uninfected red oaks before they become infected c Trench around the infected tree d Prune the infected red oak before it spreads it to the others

12 A year is divided into three distinct categories for oak pruning and the overland spread of oak wilt by beetles- high risk

low risk and safe period The ldquolow risk periodrdquo is associated with a November December January b January February March c April May June d July August September October

13 Which of the following trees can be identified by the distinct alternating bands of light and dark colored bark a American elm and rock elm b Siberian elm c Red elm and rock elm d All of the above

14 How many times during the growing season should a Tree inspector check for Dutch elm disease symptoms on elm trees a At least once b At least twice c At least three times d At least four times

15 Sapwood staining or discoloration is a common symptom of Dutch elm disease a True b False

16 Dutch elm disease can be found on a American and Siberian elm b Rock and red elm c Red and American elm d All of the above

17 Dutch elm disease can be spread by root grafts and a Insects chewing through the bark of young branch unions b Insects transported by wood chips from diseased elm trees c Spores carried by wind d Spores carried by rain

18 Native elm bark beetles normally have _____ generation(s) in one year in Minnesota a 1 b 2 c 3 d 4

19 European elm bark beetles overwinter as a Adults b Pupae c Juveniles d Larvae

20 All dead and dying elm trees from the previous year must be removed and properly disposed or treated prior to April 1st a True b False

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

• complete with cover for digital copy
• • ti study packet web cover 2012
  • ti study packet complete less cover
  • • ti study packet contents 2012
    • IdentifyandManageDutchElmDisease
    • DEDmanagement
    • DEDfuture
    • OakWiltinMinnesota
    • OW root graft control barriers
    • Control DEDvsOW
    • OWDEDTimetable
    • EmeraldAshBorer Jeff Hahn
    • ForestTentCaterpillar PEST ALERT
    • BUR OAK BLIGHT PEST ALERT
    • Amer and otiental bittersweet id USGS
    • • Invasive species are one of the greatest threats to native ecosystems They can crowd out native species and change the natural nutrient cycling processes that take place in ecosystems13
      • • thousand_cankers_disease_print_res
        • Web Sites3
        • • studyExamFinal
          • studyExamAnswers

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Thousand Cankers Disease

United StatesDepartment of Agriculture

Forest ServiceNortheastern Area

State and Private ForestryNAndashPRndash02ndash10

October 2011 (revised)

Dieback and mortality of eastern black walnut (Juglans nigra) in several Western States have become more common and severe during the last decade A tiny bark beetle is creating numerous galleries beneath the bark of affected branches resulting in fungal infection and canker formation The large numbers of cankers associated with dead branches suggest the diseasersquos namemdashthousand cankers disease

The principal agents involved in this disease are a newly identified fungus (Geosmithia sp with a proposed name of Geosmithia morbida) and the walnut twig beetle (Pityophthorus juglandis) Both the fungus and the beetle only occur on walnut species An infested tree usually dies within 3 years of initial symptoms

Thousand cankers disease has been found in many Western States (figure 1) The fungus and the beetle have not been found east of the Great Plains However a number of factors suggest that this disease could establish in eastern forests the widespread distribution of eastern black walnut the susceptibility of this tree species to the disease and the capacity of the fungus and beetle to invade new areas and survive under a wide range of climatic conditions in the West

Disease SymptomsThe three major symptoms of this disease are branch mortality numerous small cankers on branches and the bole and evidence of tiny bark beetles The earliest symptom is yellowing foliage that progresses rapidly to brown wilted foliage then finally branch mortality (figure 2) The fungus causes distinctive circular to oblong cankers in the phloem under the bark which eventually kill the cambium (figure 3) The bark surface may have no symptoms or a dark amber stain or cracking of the bark may occur directly above a canker Numerous tiny bark beetle entrance and exit holes are visible on dead and dying branches (figure 4) and bark beetle galleries are often found within the cankers In the final stages of disease even the main stem has beetle attacks and cankers

Geosmithia spMembers of the genus Geosmithia have not been considered to be important plant pathogens but Geosmithia morbida appears to be more virulent than

Figure 1 Thousand cankers disease occurs in 9 western states the year in which the disease was confirmed is noted Since 2010 TCD has been found in three locations in the East (TN VA PA - see ) The native ranges of eastern black walnut (dark green) and four western black walnut species (light green) are shown Eastern black walnut is widely planted in the West but is not depicted on this map

Figure 2 Wilting black walnut in the last stages of thousand cankers disease

Figure 3 Small branch cankers caused by Geosmithia morbida

Published by USDA Forest Service Northeastern Area State and Private Forestry 11 Campus Boulevard Newtown Square PA 19073 wwwnafsfedus

Federal Recycling ProgramPrinted on recycled paper

USDA is an equal opportunity provider and employer

related species Aside from causing cankers the fungus is inconspicuous Culturing on agar media is required to confirm its identity Adult bark beetles carry fungal spores that are then introduced into the phloem when they construct galleries Small cankers develop around the galleries these cankers may enlarge and coalesce to completely girdle the branch Trees die as a result of these canker infections at each of the thousands of beetle attack sites

Walnut Twig BeetleThe walnut twig beetle is native to Arizona California and New Mexico It has invaded Colorado Idaho Oregon Utah and Washington where walnuts have been widely planted The beetle has not caused significant branch mortality by itself Through its association with this newly identified fungus it appears to have greatly increased in abundance Adult beetles are very small (15 to 20 mm long or about 116 in) and are reddish brown in color (figure 5) This species is a typical-looking bark beetle that is characterized by its very small size and four to six concentric ridges on the upper surface of the pronotum (the shield-like cover behind and over the head) (figure 5A) Like most bark beetles the larvae are white C shaped and found in the phloem For this species the egg galleries created by the adults are horizontal (across the grain) and the larval galleries tend to be vertical (along the grain) (figure 6)

Survey and SamplesVisually inspecting walnut trees for dieback is currently the best survey tool for the Eastern United States Look for declining trees with the symptoms described above If you suspect that your walnut trees have thousand cankers disease collect a branch 2 to 4 inches

Figure 4 Exit holes made by adult walnut twig beetles

in diameter and 6 to 12 inches long that has visible symptoms Please submit branch samples to your Statersquos plant diagnostic clinic Each State has a clinic that is part of the National Plant Diagnostic Network (NPDN) They can be found at the NPDN Web site (wwwnpdnorg) You may also contact your State Department of Agriculture State Forester or Cooperative Extension Office for assistance

Prepared by Steven Seybold Research Entomologist US Forest Service Pacific Southwest Research StationDennis Haugen Forest Entomologist and Joseph OrsquoBrien Plant Pathologist US Forest Service Northeastern Area State and Private ForestryAndrew Graves Postdoctoral Research Associate UC-Davis Department of Plant Pathology

Photographs Figure 1 Andrew GravesFigure 2 Manfred Mielke US Forest Service Figures 3 4 6 Whitney Cranshaw Colorado State University wwwforestryimagesorg Figure 5 Steve Valley Oregon Department of Agriculture

Figure 6 Walnut twig beetle galleries under the bark of a large branch

Figure 5 Walnut twig beetle top view (A) and side view (B)

18 mm

A

B

Websites to study and look through Click on link address to view publication

How to Manage DED

httpwwwnafsfedusspfopubshowtosht_dedht_dedhtm

Oak Wilt in Minnesota

httpwwwextensionumnedudistributionnaturalresourcesDD3174html

Forest Tent Caterpillar

httpwwwnafsfedusspfopubspest_alftcftchtm

Gypsy moth information

httpwwwmdastatemnusplantspestmanagementgmunitgmhistoryaspx

Gypsy Moth Life Cycle

httpwwwmdastatemnusenplantspestmanagementgmunitgmbiologyaspx

Save our Ash

httpwwwmdastatemnusplantspestmanagementeabaspx

Signs and Symptoms of the Emerald Ash Borer httpwwwtwpindependencemiusServicesPublicWorksEnvironmentalNewsE2938pdf

Whatrsquos In That Wood Pile

httpwwwagdepartmentcomProgramsppEABFilesWhatsInThatWoodPilepdf

Practice Tree Inspector Certification Exam Answers to these questions can be found in readings in the study packet

These practice questions will give you an idea on the types of topics level of difficulty and format of questions to expect in the exam

1 Firewood restrictions are in place to reduce the spread of a Ash plant bug b Emerald ash borer c Ash flower gall d Ash rust

2 ldquoAvoidedrdquo food of a gypsy moth includes a beech buckeye hornbeam maple b ash catalpa dogwood locust c spruce pine larch d aspen oak poplar willow

3 Gypsy moths are established in Minnesota

a True b False

4 Signs of emerald ash borer attack on standing trees or firewood logs include a O-shaped exit holes b D-shaped exit holes c S-shaped galleries in the sapwood under the bark d Y-shaped galleries in the sapwood under the bark e A and D f B and C

5 Forest tent caterpillars prefer to feed on the following group of trees a Elms oaks pine species b Ash cherry spruce species c Red maple and sycamore d Basswood birch sugar maple

6 The forest tent caterpillar damage does not usually cause mortality in trees but if management is desired it should include one of the following management strategies

a Pyridaben applications b Bifenthrin applications c Bacillus thuringiensis applications d Dicofol applications

7 Oak wilt can be spread by root grafts and a Insects chewing into bark b Insects attracted to fresh pruning wounds c Spores carried by wind d Spores carried by rain

8 Oak wilt is a disease caused by the pathogen a Ceratosystis fagacearum b Ophiostpma ulmi c oak bark beetle d oak leaf beetle

9 A red oak tree that is infected will generally completely wilt within this time frame a 1 week b 1-2 weeks c 2-6 weeks d 4-8 weeks

10 What is the percentage of oak wilt disease spread through root grafts a 10 b 30 c 60 d 90

11 If you identify a red oak tree with oak wilt that has several uninfected red oaks surrounding it you should first a Remove the infected tree as soon as possible b Prune the uninfected red oaks before they become infected c Trench around the infected tree d Prune the infected red oak before it spreads it to the others

12 A year is divided into three distinct categories for oak pruning and the overland spread of oak wilt by beetles- high risk

low risk and safe period The ldquolow risk periodrdquo is associated with a November December January b January February March c April May June d July August September October

13 Which of the following trees can be identified by the distinct alternating bands of light and dark colored bark a American elm and rock elm b Siberian elm c Red elm and rock elm d All of the above

14 How many times during the growing season should a Tree inspector check for Dutch elm disease symptoms on elm trees a At least once b At least twice c At least three times d At least four times

15 Sapwood staining or discoloration is a common symptom of Dutch elm disease a True b False

16 Dutch elm disease can be found on a American and Siberian elm b Rock and red elm c Red and American elm d All of the above

17 Dutch elm disease can be spread by root grafts and a Insects chewing through the bark of young branch unions b Insects transported by wood chips from diseased elm trees c Spores carried by wind d Spores carried by rain

18 Native elm bark beetles normally have _____ generation(s) in one year in Minnesota a 1 b 2 c 3 d 4

19 European elm bark beetles overwinter as a Adults b Pupae c Juveniles d Larvae

20 All dead and dying elm trees from the previous year must be removed and properly disposed or treated prior to April 1st a True b False

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

• complete with cover for digital copy
• • ti study packet web cover 2012
  • ti study packet complete less cover
  • • ti study packet contents 2012
    • IdentifyandManageDutchElmDisease
    • DEDmanagement
    • DEDfuture
    • OakWiltinMinnesota
    • OW root graft control barriers
    • Control DEDvsOW
    • OWDEDTimetable
    • EmeraldAshBorer Jeff Hahn
    • ForestTentCaterpillar PEST ALERT
    • BUR OAK BLIGHT PEST ALERT
    • Amer and otiental bittersweet id USGS
    • • Invasive species are one of the greatest threats to native ecosystems They can crowd out native species and change the natural nutrient cycling processes that take place in ecosystems13
      • • thousand_cankers_disease_print_res
        • Web Sites3
        • • studyExamFinal
          • studyExamAnswers

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Published by USDA Forest Service Northeastern Area State and Private Forestry 11 Campus Boulevard Newtown Square PA 19073 wwwnafsfedus

Federal Recycling ProgramPrinted on recycled paper

USDA is an equal opportunity provider and employer

related species Aside from causing cankers the fungus is inconspicuous Culturing on agar media is required to confirm its identity Adult bark beetles carry fungal spores that are then introduced into the phloem when they construct galleries Small cankers develop around the galleries these cankers may enlarge and coalesce to completely girdle the branch Trees die as a result of these canker infections at each of the thousands of beetle attack sites

Walnut Twig BeetleThe walnut twig beetle is native to Arizona California and New Mexico It has invaded Colorado Idaho Oregon Utah and Washington where walnuts have been widely planted The beetle has not caused significant branch mortality by itself Through its association with this newly identified fungus it appears to have greatly increased in abundance Adult beetles are very small (15 to 20 mm long or about 116 in) and are reddish brown in color (figure 5) This species is a typical-looking bark beetle that is characterized by its very small size and four to six concentric ridges on the upper surface of the pronotum (the shield-like cover behind and over the head) (figure 5A) Like most bark beetles the larvae are white C shaped and found in the phloem For this species the egg galleries created by the adults are horizontal (across the grain) and the larval galleries tend to be vertical (along the grain) (figure 6)

Survey and SamplesVisually inspecting walnut trees for dieback is currently the best survey tool for the Eastern United States Look for declining trees with the symptoms described above If you suspect that your walnut trees have thousand cankers disease collect a branch 2 to 4 inches

Figure 4 Exit holes made by adult walnut twig beetles

in diameter and 6 to 12 inches long that has visible symptoms Please submit branch samples to your Statersquos plant diagnostic clinic Each State has a clinic that is part of the National Plant Diagnostic Network (NPDN) They can be found at the NPDN Web site (wwwnpdnorg) You may also contact your State Department of Agriculture State Forester or Cooperative Extension Office for assistance

Prepared by Steven Seybold Research Entomologist US Forest Service Pacific Southwest Research StationDennis Haugen Forest Entomologist and Joseph OrsquoBrien Plant Pathologist US Forest Service Northeastern Area State and Private ForestryAndrew Graves Postdoctoral Research Associate UC-Davis Department of Plant Pathology

Photographs Figure 1 Andrew GravesFigure 2 Manfred Mielke US Forest Service Figures 3 4 6 Whitney Cranshaw Colorado State University wwwforestryimagesorg Figure 5 Steve Valley Oregon Department of Agriculture

Figure 6 Walnut twig beetle galleries under the bark of a large branch

Figure 5 Walnut twig beetle top view (A) and side view (B)

18 mm

A

B

Websites to study and look through Click on link address to view publication

How to Manage DED

httpwwwnafsfedusspfopubshowtosht_dedht_dedhtm

Oak Wilt in Minnesota

httpwwwextensionumnedudistributionnaturalresourcesDD3174html

Forest Tent Caterpillar

httpwwwnafsfedusspfopubspest_alftcftchtm

Gypsy moth information

httpwwwmdastatemnusplantspestmanagementgmunitgmhistoryaspx

Gypsy Moth Life Cycle

httpwwwmdastatemnusenplantspestmanagementgmunitgmbiologyaspx

Save our Ash

httpwwwmdastatemnusplantspestmanagementeabaspx

Signs and Symptoms of the Emerald Ash Borer httpwwwtwpindependencemiusServicesPublicWorksEnvironmentalNewsE2938pdf

Whatrsquos In That Wood Pile

httpwwwagdepartmentcomProgramsppEABFilesWhatsInThatWoodPilepdf

Practice Tree Inspector Certification Exam Answers to these questions can be found in readings in the study packet

These practice questions will give you an idea on the types of topics level of difficulty and format of questions to expect in the exam

1 Firewood restrictions are in place to reduce the spread of a Ash plant bug b Emerald ash borer c Ash flower gall d Ash rust

2 ldquoAvoidedrdquo food of a gypsy moth includes a beech buckeye hornbeam maple b ash catalpa dogwood locust c spruce pine larch d aspen oak poplar willow

3 Gypsy moths are established in Minnesota

a True b False

4 Signs of emerald ash borer attack on standing trees or firewood logs include a O-shaped exit holes b D-shaped exit holes c S-shaped galleries in the sapwood under the bark d Y-shaped galleries in the sapwood under the bark e A and D f B and C

5 Forest tent caterpillars prefer to feed on the following group of trees a Elms oaks pine species b Ash cherry spruce species c Red maple and sycamore d Basswood birch sugar maple

6 The forest tent caterpillar damage does not usually cause mortality in trees but if management is desired it should include one of the following management strategies

a Pyridaben applications b Bifenthrin applications c Bacillus thuringiensis applications d Dicofol applications

7 Oak wilt can be spread by root grafts and a Insects chewing into bark b Insects attracted to fresh pruning wounds c Spores carried by wind d Spores carried by rain

8 Oak wilt is a disease caused by the pathogen a Ceratosystis fagacearum b Ophiostpma ulmi c oak bark beetle d oak leaf beetle

9 A red oak tree that is infected will generally completely wilt within this time frame a 1 week b 1-2 weeks c 2-6 weeks d 4-8 weeks

10 What is the percentage of oak wilt disease spread through root grafts a 10 b 30 c 60 d 90

11 If you identify a red oak tree with oak wilt that has several uninfected red oaks surrounding it you should first a Remove the infected tree as soon as possible b Prune the uninfected red oaks before they become infected c Trench around the infected tree d Prune the infected red oak before it spreads it to the others

12 A year is divided into three distinct categories for oak pruning and the overland spread of oak wilt by beetles- high risk

low risk and safe period The ldquolow risk periodrdquo is associated with a November December January b January February March c April May June d July August September October

13 Which of the following trees can be identified by the distinct alternating bands of light and dark colored bark a American elm and rock elm b Siberian elm c Red elm and rock elm d All of the above

14 How many times during the growing season should a Tree inspector check for Dutch elm disease symptoms on elm trees a At least once b At least twice c At least three times d At least four times

15 Sapwood staining or discoloration is a common symptom of Dutch elm disease a True b False

16 Dutch elm disease can be found on a American and Siberian elm b Rock and red elm c Red and American elm d All of the above

17 Dutch elm disease can be spread by root grafts and a Insects chewing through the bark of young branch unions b Insects transported by wood chips from diseased elm trees c Spores carried by wind d Spores carried by rain

18 Native elm bark beetles normally have _____ generation(s) in one year in Minnesota a 1 b 2 c 3 d 4

19 European elm bark beetles overwinter as a Adults b Pupae c Juveniles d Larvae

20 All dead and dying elm trees from the previous year must be removed and properly disposed or treated prior to April 1st a True b False

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

• complete with cover for digital copy
• • ti study packet web cover 2012
  • ti study packet complete less cover
  • • ti study packet contents 2012
    • IdentifyandManageDutchElmDisease
    • DEDmanagement
    • DEDfuture
    • OakWiltinMinnesota
    • OW root graft control barriers
    • Control DEDvsOW
    • OWDEDTimetable
    • EmeraldAshBorer Jeff Hahn
    • ForestTentCaterpillar PEST ALERT
    • BUR OAK BLIGHT PEST ALERT
    • Amer and otiental bittersweet id USGS
    • • Invasive species are one of the greatest threats to native ecosystems They can crowd out native species and change the natural nutrient cycling processes that take place in ecosystems13
      • • thousand_cankers_disease_print_res
        • Web Sites3
        • • studyExamFinal
          • studyExamAnswers

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Websites to study and look through Click on link address to view publication

How to Manage DED

httpwwwnafsfedusspfopubshowtosht_dedht_dedhtm

Oak Wilt in Minnesota

httpwwwextensionumnedudistributionnaturalresourcesDD3174html

Forest Tent Caterpillar

httpwwwnafsfedusspfopubspest_alftcftchtm

Gypsy moth information

httpwwwmdastatemnusplantspestmanagementgmunitgmhistoryaspx

Gypsy Moth Life Cycle

httpwwwmdastatemnusenplantspestmanagementgmunitgmbiologyaspx

Save our Ash

httpwwwmdastatemnusplantspestmanagementeabaspx

Signs and Symptoms of the Emerald Ash Borer httpwwwtwpindependencemiusServicesPublicWorksEnvironmentalNewsE2938pdf

Whatrsquos In That Wood Pile

httpwwwagdepartmentcomProgramsppEABFilesWhatsInThatWoodPilepdf

Practice Tree Inspector Certification Exam Answers to these questions can be found in readings in the study packet

These practice questions will give you an idea on the types of topics level of difficulty and format of questions to expect in the exam

1 Firewood restrictions are in place to reduce the spread of a Ash plant bug b Emerald ash borer c Ash flower gall d Ash rust

2 ldquoAvoidedrdquo food of a gypsy moth includes a beech buckeye hornbeam maple b ash catalpa dogwood locust c spruce pine larch d aspen oak poplar willow

3 Gypsy moths are established in Minnesota

a True b False

4 Signs of emerald ash borer attack on standing trees or firewood logs include a O-shaped exit holes b D-shaped exit holes c S-shaped galleries in the sapwood under the bark d Y-shaped galleries in the sapwood under the bark e A and D f B and C

5 Forest tent caterpillars prefer to feed on the following group of trees a Elms oaks pine species b Ash cherry spruce species c Red maple and sycamore d Basswood birch sugar maple

6 The forest tent caterpillar damage does not usually cause mortality in trees but if management is desired it should include one of the following management strategies

a Pyridaben applications b Bifenthrin applications c Bacillus thuringiensis applications d Dicofol applications

7 Oak wilt can be spread by root grafts and a Insects chewing into bark b Insects attracted to fresh pruning wounds c Spores carried by wind d Spores carried by rain

8 Oak wilt is a disease caused by the pathogen a Ceratosystis fagacearum b Ophiostpma ulmi c oak bark beetle d oak leaf beetle

9 A red oak tree that is infected will generally completely wilt within this time frame a 1 week b 1-2 weeks c 2-6 weeks d 4-8 weeks

10 What is the percentage of oak wilt disease spread through root grafts a 10 b 30 c 60 d 90

11 If you identify a red oak tree with oak wilt that has several uninfected red oaks surrounding it you should first a Remove the infected tree as soon as possible b Prune the uninfected red oaks before they become infected c Trench around the infected tree d Prune the infected red oak before it spreads it to the others

12 A year is divided into three distinct categories for oak pruning and the overland spread of oak wilt by beetles- high risk

low risk and safe period The ldquolow risk periodrdquo is associated with a November December January b January February March c April May June d July August September October

13 Which of the following trees can be identified by the distinct alternating bands of light and dark colored bark a American elm and rock elm b Siberian elm c Red elm and rock elm d All of the above

14 How many times during the growing season should a Tree inspector check for Dutch elm disease symptoms on elm trees a At least once b At least twice c At least three times d At least four times

15 Sapwood staining or discoloration is a common symptom of Dutch elm disease a True b False

16 Dutch elm disease can be found on a American and Siberian elm b Rock and red elm c Red and American elm d All of the above

17 Dutch elm disease can be spread by root grafts and a Insects chewing through the bark of young branch unions b Insects transported by wood chips from diseased elm trees c Spores carried by wind d Spores carried by rain

18 Native elm bark beetles normally have _____ generation(s) in one year in Minnesota a 1 b 2 c 3 d 4

19 European elm bark beetles overwinter as a Adults b Pupae c Juveniles d Larvae

20 All dead and dying elm trees from the previous year must be removed and properly disposed or treated prior to April 1st a True b False

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

• complete with cover for digital copy
• • ti study packet web cover 2012
  • ti study packet complete less cover
  • • ti study packet contents 2012
    • IdentifyandManageDutchElmDisease
    • DEDmanagement
    • DEDfuture
    • OakWiltinMinnesota
    • OW root graft control barriers
    • Control DEDvsOW
    • OWDEDTimetable
    • EmeraldAshBorer Jeff Hahn
    • ForestTentCaterpillar PEST ALERT
    • BUR OAK BLIGHT PEST ALERT
    • Amer and otiental bittersweet id USGS
    • • Invasive species are one of the greatest threats to native ecosystems They can crowd out native species and change the natural nutrient cycling processes that take place in ecosystems13
      • • thousand_cankers_disease_print_res
        • Web Sites3
        • • studyExamFinal
          • studyExamAnswers

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Practice Tree Inspector Certification Exam Answers to these questions can be found in readings in the study packet

These practice questions will give you an idea on the types of topics level of difficulty and format of questions to expect in the exam

1 Firewood restrictions are in place to reduce the spread of a Ash plant bug b Emerald ash borer c Ash flower gall d Ash rust

2 ldquoAvoidedrdquo food of a gypsy moth includes a beech buckeye hornbeam maple b ash catalpa dogwood locust c spruce pine larch d aspen oak poplar willow

3 Gypsy moths are established in Minnesota

a True b False

4 Signs of emerald ash borer attack on standing trees or firewood logs include a O-shaped exit holes b D-shaped exit holes c S-shaped galleries in the sapwood under the bark d Y-shaped galleries in the sapwood under the bark e A and D f B and C

5 Forest tent caterpillars prefer to feed on the following group of trees a Elms oaks pine species b Ash cherry spruce species c Red maple and sycamore d Basswood birch sugar maple

6 The forest tent caterpillar damage does not usually cause mortality in trees but if management is desired it should include one of the following management strategies

a Pyridaben applications b Bifenthrin applications c Bacillus thuringiensis applications d Dicofol applications

7 Oak wilt can be spread by root grafts and a Insects chewing into bark b Insects attracted to fresh pruning wounds c Spores carried by wind d Spores carried by rain

8 Oak wilt is a disease caused by the pathogen a Ceratosystis fagacearum b Ophiostpma ulmi c oak bark beetle d oak leaf beetle

9 A red oak tree that is infected will generally completely wilt within this time frame a 1 week b 1-2 weeks c 2-6 weeks d 4-8 weeks

10 What is the percentage of oak wilt disease spread through root grafts a 10 b 30 c 60 d 90

11 If you identify a red oak tree with oak wilt that has several uninfected red oaks surrounding it you should first a Remove the infected tree as soon as possible b Prune the uninfected red oaks before they become infected c Trench around the infected tree d Prune the infected red oak before it spreads it to the others

12 A year is divided into three distinct categories for oak pruning and the overland spread of oak wilt by beetles- high risk

low risk and safe period The ldquolow risk periodrdquo is associated with a November December January b January February March c April May June d July August September October

13 Which of the following trees can be identified by the distinct alternating bands of light and dark colored bark a American elm and rock elm b Siberian elm c Red elm and rock elm d All of the above

14 How many times during the growing season should a Tree inspector check for Dutch elm disease symptoms on elm trees a At least once b At least twice c At least three times d At least four times

15 Sapwood staining or discoloration is a common symptom of Dutch elm disease a True b False

16 Dutch elm disease can be found on a American and Siberian elm b Rock and red elm c Red and American elm d All of the above

17 Dutch elm disease can be spread by root grafts and a Insects chewing through the bark of young branch unions b Insects transported by wood chips from diseased elm trees c Spores carried by wind d Spores carried by rain

18 Native elm bark beetles normally have _____ generation(s) in one year in Minnesota a 1 b 2 c 3 d 4

19 European elm bark beetles overwinter as a Adults b Pupae c Juveniles d Larvae

20 All dead and dying elm trees from the previous year must be removed and properly disposed or treated prior to April 1st a True b False

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

• complete with cover for digital copy
• • ti study packet web cover 2012
  • ti study packet complete less cover
  • • ti study packet contents 2012
    • IdentifyandManageDutchElmDisease
    • DEDmanagement
    • DEDfuture
    • OakWiltinMinnesota
    • OW root graft control barriers
    • Control DEDvsOW
    • OWDEDTimetable
    • EmeraldAshBorer Jeff Hahn
    • ForestTentCaterpillar PEST ALERT
    • BUR OAK BLIGHT PEST ALERT
    • Amer and otiental bittersweet id USGS
    • • Invasive species are one of the greatest threats to native ecosystems They can crowd out native species and change the natural nutrient cycling processes that take place in ecosystems13
      • • thousand_cankers_disease_print_res
        • Web Sites3
        • • studyExamFinal
          • studyExamAnswers

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10 What is the percentage of oak wilt disease spread through root grafts a 10 b 30 c 60 d 90

11 If you identify a red oak tree with oak wilt that has several uninfected red oaks surrounding it you should first a Remove the infected tree as soon as possible b Prune the uninfected red oaks before they become infected c Trench around the infected tree d Prune the infected red oak before it spreads it to the others

12 A year is divided into three distinct categories for oak pruning and the overland spread of oak wilt by beetles- high risk

low risk and safe period The ldquolow risk periodrdquo is associated with a November December January b January February March c April May June d July August September October

13 Which of the following trees can be identified by the distinct alternating bands of light and dark colored bark a American elm and rock elm b Siberian elm c Red elm and rock elm d All of the above

14 How many times during the growing season should a Tree inspector check for Dutch elm disease symptoms on elm trees a At least once b At least twice c At least three times d At least four times

15 Sapwood staining or discoloration is a common symptom of Dutch elm disease a True b False

16 Dutch elm disease can be found on a American and Siberian elm b Rock and red elm c Red and American elm d All of the above

17 Dutch elm disease can be spread by root grafts and a Insects chewing through the bark of young branch unions b Insects transported by wood chips from diseased elm trees c Spores carried by wind d Spores carried by rain

18 Native elm bark beetles normally have _____ generation(s) in one year in Minnesota a 1 b 2 c 3 d 4

19 European elm bark beetles overwinter as a Adults b Pupae c Juveniles d Larvae

20 All dead and dying elm trees from the previous year must be removed and properly disposed or treated prior to April 1st a True b False

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

• complete with cover for digital copy
• • ti study packet web cover 2012
  • ti study packet complete less cover
  • • ti study packet contents 2012
    • IdentifyandManageDutchElmDisease
    • DEDmanagement
    • DEDfuture
    • OakWiltinMinnesota
    • OW root graft control barriers
    • Control DEDvsOW
    • OWDEDTimetable
    • EmeraldAshBorer Jeff Hahn
    • ForestTentCaterpillar PEST ALERT
    • BUR OAK BLIGHT PEST ALERT
    • Amer and otiental bittersweet id USGS
    • • Invasive species are one of the greatest threats to native ecosystems They can crowd out native species and change the natural nutrient cycling processes that take place in ecosystems13
      • • thousand_cankers_disease_print_res
        • Web Sites3
        • • studyExamFinal
          • studyExamAnswers

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Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

Answers for Practice Tree Inspector Certification Exam

1 b 2 b 3 b 4 f 5 d 6 c 7 b 8 a 9 c 10 d 11 c 12 d 13 a 14 c 15 a 16 d 17 a 18 a 19 d 20 a

• complete with cover for digital copy
• • ti study packet web cover 2012
  • ti study packet complete less cover
  • • ti study packet contents 2012
    • IdentifyandManageDutchElmDisease
    • DEDmanagement
    • DEDfuture
    • OakWiltinMinnesota
    • OW root graft control barriers
    • Control DEDvsOW
    • OWDEDTimetable
    • EmeraldAshBorer Jeff Hahn
    • ForestTentCaterpillar PEST ALERT
    • BUR OAK BLIGHT PEST ALERT
    • Amer and otiental bittersweet id USGS
    • • Invasive species are one of the greatest threats to native ecosystems They can crowd out native species and change the natural nutrient cycling processes that take place in ecosystems13
      • • thousand_cankers_disease_print_res
        • Web Sites3
        • • studyExamFinal
          • studyExamAnswers

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