for Arborists, Landscape Managers & Nursery Managers

Commercial Horticulture August 23, 2013Coordinator Weekly IPM report: Stanton Gill, Extension Specialist, IPM for Nursery, Greenhouse and Managed Landscapes, sgill@umd.edu. 301-596-9413 (office) or 410-868-9400 (cell)

Regular Contributors: Pest and Beneficial Insect Information: Stanton Gill and Paula Shrewsbury (Extension Specialists) Disease Information: Karen Rane (Plant Pathologist) and David Clement (Extension Specialist)Weed of the Week: Chuck Schuster (Extension Educator, Montgomery County)Cultural Information: Ginny Rosenkranz (Extension Educator, Wicomico/Worcester/Somerset Counties)Fertility Management: Andrew Ristvey (Regional Specialist, Wye Research & Education Center)Design, Layout and Editing: Suzanne Klick (Technician, CMREC)

In This Issue...

If you work for a commercial horticultural business in the area, you can report insect, disease, weed or cultural

plant problems found in the landscape or nursery to

sklick@umd.edu

TPM/IPM Weekly Report

- Wet weather- Early defoliation- Spider mites for research- Lawn fertilizer law review sessions and testing- Weed control in nurseries- Scale updates- Brown marmorated stink bug update- Scarab beetle grubs- Cyanobacteria- Impatiens downy mildew- Zelkovas and branch drop- Caterpillars- Bagworms- Snowy tree cricket- Fun photo

Beneficial of the WeekWeed of the WeekPlant of the WeekDegree DaysPhenologyAnnouncements

A New Address for IPMnet

Integrated Pest Management for

Commercial Horticultureextension.umd.edu/ipm

Wet WeatherThis season is one of the wettest summers since 2004 when new records were set for the East Coast. In southern states they are seeing even more rain than our area with fields remaining underwater for extended periods. Some of the people in Kentucky are finding crayfish moving into lawns and golf course fairways. The crayfish dig down into the moist ground and make a chimney mound project upward. You know it is wet for too long when crayfish move into lawns.

Early DefoliationWe are receiving reports that Amelanchier is defoliating early this year in both landscapes and nurseries. There is also spotting on foliage which is probably tied into the rains this year. There is nothing to do about it.

Plants With Spider Mites Needed for ResearchPaula Shrewsbury and Nancy Harding are in need of spider mites to conduct a research trial. This could be twospotted spider mite, boxwood spider mite,

southern red mite, etc.

They need 15 to 20 plants with mites and plants can be in nurseries or landscapes. If you possibly have a site contact Nancy Harding at nharding@

umd.edu. Thanks.

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Lawn Fertilizer Law Information on Maryland’s Lawn Fertilizer Lawn including review sessions and testing dates and a pdf version of The Professional Lawn Care Manual are available at: http://mda.maryland.gov/fertilizer The requirement for certification is October, 2013. Review sessions and testing dates are listed below:

Review Dates and Locations: There is no cost to attend, however, seating is limited and pre-registration is required. The review sessions are not designed as training sessions. Please do not attend the review session if you have not read the manual.

Testing Dates and Locations:

Easton DerwoodSeptember 18, 12:30-2:30 pm September 11, noon-2:00 pmSeptember 18, 3:00-5:00 pm September 11, 2:30-4:30 pm

Montgomery CountySeptember 11, 20139:00 a.m. – 11:30 a.m.University of Maryland ExtensionAgricultural Farm History Park18410 Muncaster RoadDerwood, MD 20855

EastonSeptember 18, 20139:30 – noonTalbot County Free Library100 West Dover StreetEaston, MD 21601

Weed Control in Nurseries

We asked Jeff Derr, Virginia Tech Experiment Station, to comment on weed control in Nurseries. Here is his response:Glyphosate can cause bark splitting and/or cankering on bark of young trees (those with a green or very thin bark). Use precaution especially late in the season. Growers should incorporate preemergence herbicide use. I would treat very early in late winter or early spring prior to germination of summer annuals, say late February. This will reduce the need for postemergence herbicides. With just scattered emerged weeds to deal with, a grower could go out with a backpack sprayer for applying glyphosate or diquat, thus having better control of the spray. Gallery plus Barricade would be one option in young trees. Growers should apply a preemergence in late August for control of winter annual weeds. Once trees are in the ground a year they can incorporate SureGuard into the program instead of Gallery. SureGuard will give some burndown of small weeds plus give better broadleaf weed control than Gallery. Growers could consider using growing tubes or other protection on the tree trunks to prevent herbicide spray from reaching the bark. Growers should cut off tree suckers - either immediately after glyphosate has been applied, or a week or 2 prior to glyphosate application, especially when applying glyphosate in late summer or fall.

Erechtites hieracifolia (Fireweed, American burnweed, or Pilewort)

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Scale Updates

White prunicola scale (WPS, armored scale): Monitoring WPS in Laytonsville on Wednesday August 21 found NO signs of crawler activity. The Degree Days per weatherchannel.com were 2542 DD. We will continue to monitor for 3rd generation crawlers.

Japanese maple scale (JMS, armored scale): Monitoring JMS in Laytonsville on Wednesday August 21 found a high percentage (over 50%) of crawlers and newly settled crawlers. The Degree Days per weatherchannel.com were 2542 DD. Based on our research and continued monitoring of JMS, crawler emergence period extend over a long period of time. Therefore, if the degree day accumulations in your area are near or at 2542 DD, you should monitor plants infested with JMS. If crawlers are present now we recommend waiting a week or two for peak crawler emergence which would be the best timing for control applications. Control: We suggest using either Distance or Talus insect growth regulators since they are effective and have the least negative impact on beneficial organisms.

To aid in your monitoring and management of JMS see fact sheets:

Japanese Maple Scale - Woody Ornamental Host Plantshttps://www.extension.umd.edu/ipm/publications/landscape-publications

Japanese Maple Scale - A Pest of Landscape Trees and Shrubshttps://www.extension.umd.edu/sites/default/files/_docs/programs/ipmnet/JapaneseMapleScale-UMD-1.pdf

Fletcher ScaleNorm Brady, Bartlett Tree Experts, sent in a sample of Eastern red cedar with Fletcher scale, Parthenolecanium fletcheri. The scale attacks Taxus, arborvitae and junipers. The crawlers were produced back in early summer, and you will find mainly 2nd instars present at this time of year. Control: This scale con be controlled using soil or basal bark sprays of a neonicotoid. This fall in late October to early November, a 2% horticultural oil can be applied to suppress the population.

Fletcher scale on Eastern red cedar

Brown Marmorated Stink Bug UpdateWe are finding all stages of brown marmorated stink bugs this week. Nymphs are the stage being found in the highest numbers. Leigh Cochrane found an egg mass with first instar stink bugs present. Here at the research center in Ellicott City, the stink bugs are still heavily infesting Hibiscus moscheotos, but we are also finding them on crabapple and bronze fennel this week.

A recently molted mid instar stink bug is white

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Grubs are Plentiful in Lawns During This Wet SummerHere in Maryland, the high soil moisture is providing perfect conditions for white grubs to survive. We are finding larvae of European chafers, Japanese beetles, Asiatic garden beetles, green June beetles, May and June beetles, and oriental beetles. The various species can be identified by examining the raster pattern (hair pattern) on the tip of the abdomen.

Because we have the high moisture levels much of the damage being done by these beetle grubs is being masked over at this point. They sever the roots of the grass, but the high moisture helps keep the grass from browning. To monitor, use a shovel to cut away a patch of grass and roots. The white grubs will be present in the root zone of the turfgrass in August.

Insect Parasitic Nematodes: Take advantage of this wet weatherIf you are going to try entomopathogenic nematodes, then a wet season like this year is a good time to try them out. Commercial preparations of insect parasitic nematodes (Steinernema and Heterorhabditis species) can suppress white grub populations under moist soil conditions. Some nematodes may work synergistically with neonicotinoid insecticides (e.g., imidacloprid or Merit) to provide greater grub control.Chemical control: Preventive control requires the use of long residual insecticides, such as imidacloprid (Merit®, Season-Long Grub Control®), thiamethoxam (Meridian®), halofenozide (Mach2®, Ortho Grub-B-Gon®, Grub-Ex®), clothianidin (Arena®), or chlorantraniliprole (Acelepryn®). These products give good control of newly hatched grubs. The best application period is during the month or so before egg hatch until the time when very young grubs are present. We are at the stage of young larvae being present.

Green June beetle grub with arrow pointing to location of raster pattern

Cyanobacteria on mulchPhoto: Jason Sersen, Kingsdene Nurseries

Strange Blue-Green Algae (Cyanobacteria) Shows up in NurseriesA garden center in Baltimore County called in with an interesting question. It was about a slimy material growing on their sidewalks and production bed areas. Michigan State University Extension Nursery container growers over the past few years have been finding this new problem in their nursery. It is a slimy-when-wet, blue-green Nostoc spp. of algae. These are not your typical aquatic forms of algae that inhabit irrigation ponds or streams, but are ones that survive in terrestrial sites. In fact, they are not even classified now as algae but are called cyanobacteria because they can conduct photosynthesis like higher plants. They are considered to be among the most ancient organisms to inhabit the earth with some fossil records showing they have been on earth for over 3.5 billion years. The problem with these primitive cyanobacteria is their slimy nature. When wet, they cause a slip-trip hazard to workers moving plants in a container growing area. Michigan State Extension faculty have seen the organism growing on hard-packed alley ways, container ground mats, aggregate stone walkways and even concrete sidewalks in retail sales areas. The organism has the capability of manufacturing and discharging polysaccharides from their cells. These discharges form a coating that protects the cyanobacteria from stresses like drought. high and low temperatures or other conditions that allow them to survive in a nursery setting quite well. We are interested if anyone else in the state is finding this growing at their nursery or garden center. Please contact me at sgill@umd.edu.

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It’s Baaaack! Impatiens Downy Mildew (IDM)Impatiens Downy Mildew (IDM) is cropping up on Impatiens walleriana in Maryland landscapes within the past week. Those intrepid gardeners and landscapers who decided to ignore the warnings and plant garden impatiens this year have been safe from this disease for most of the season, at least in part because any plants on the market were treated with fungicides to control the disease during production. But now, most landscape plantings have “outgrown” the protection of fungicides applied in the greenhouse, and this year our unusually cool, moist summer weather is perfect for disease development. Look for slight yellow mottling or leaf curl as initial symptoms of the disease (Figure 1). Turn those leaves over, and you’ll see a white “lawn” of sporulation of the downy mildew pathogen (Figure 2). Infected leaves will drop, eventually leaving leafless green stems. Fungicides will not cure infected plants, so management involves removal and destruction of diseased plants. One way to dispose of infected plants is to send them to Dr. Jo Anne Crouch at USDA ARS in Beltsville, who is collecting isolates of IDM for research. Her website with information on sample submission can be found at http://www.ornamentalpathology.com/. Because there is the potential for the pathogen to overwinter in our area in infected plant debris, it is a good idea to avoid planting garden impatiens in the same beds next year.

Figure 1. Upper surface of impatiens leaf (arrow) with downy mildew, showing slight mottling.

Figure 2. Lower surface of same leaf showing extensive sporulation.

Branches Dropping From ZelkovaJenn Rodriquez, Ruppert Companies, and Damian Varga, Scientific Plant Service, both alerted us to zelkova that had large numbers of small branches dropping off trees in August. We examined the branch ends under a dissecting microscope and the twigs had been chewed off in a ragged pattern. These small branches were being chewed off by squirrels. Zelkova also produces a small kidney-shaped drupe and the squirrels were dropping these off the trees. Some of the drupes had small insects feeding in them. Several people feel it must be an insect that is dropping the foliage and small stems, but it is squirrel activity. We have had branch samples like this in other years, usually at the end of the summer when squirrels begin to build new nests for the fall and winter. Zelkova appears to be one of the squirrel’s favorite trees to cut off branches. So, you may see this damage with some of your customers’ trees this fall.

Small zelkova branches scattered on the ground due to squirrelsPhoto: Jenn Rodriquez, Ruppert Comapnies

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CaterpillarsLeigh Cochrane is finding milkweed tussock moth caterpillars on milkweed. Of course, the monarch caterpillar is another species that will be found on Asclepias plants.

Orangestriped oakworms continue to be active. Craig Greco, Yardbirds, Inc., found one larvae that was attached by a parasitic wasp.

Yellownecked caterpillars were found in a cluster on a crabapple leaf here at the research center in Ellicott City. These caterpillars had defoliated this tree last year. There is one generation per year, but larvae can be found from mid-summer to early fall.

Yellow bear caterpillars are fairly common in this area and have a wide host range. One was found feeding on Phlox paniculata.

Parasitized orangestriped oakwormPhoto: Craig Greco, Yardbirds, Inc.

A cluster of early instar yellownecked caterpillars (left) and a yellow bear caterpillar (above)

Steve Sullivan, The Brickman Group, found redhumped caterpillars defoliating redbud this week. This caterpillar has a wide woody plant host range. Most often, it does not occur in high numbers to be a problem, but it some years, populations can erupt and cause significant damage.

We also found saltmarsh caterpillars on sunflowers this week. For garden centers and greenhouse operations, please note that these caterpillars feeds on a wide host range which includes fall mum crops.

Control: Unless found in high numbers, control is not necessary. If larvae are small, Bt can still be used. Otherwise, you can use other products labeled for caterpillar control.

A saltmarsh caterpillar (left) and a redhumped caterpillar (right)

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Fall webworm on cherryPhoto: Connie Bowers, Garden Makeover Company

BagwormsThis summer, Debby Smith-Fiola has been monitoring bagworm activity for us. Last week she reported that the female bagworms started migrating to the top parts of plants. The males don’t really care where they hang out since they will be pupating around Labor Day. There is no real feeding activity of bagworms this late in August. Customers may notice the large bags in August, but this is not the time to control them. The bags can be hand removed, but do not waste time trying to spray for bagworms now.

Snowy tree cricket damage on euonymusPhoto: Steve Sullivan, The Brickman Group

Connie Bowers, Garden Makeover Company, noted that apparently it is a banner year for fall webworms. Connie is seeing them everywhere now. She noted that she removed many nests from Kwanzan cherry trees, ‘Forest Pansy’ redbud, and Malus sp. at a property in Silver Spring.Control: Be sure to see if there are active caterpillars in the tents. Prune out webbed terminals. There are numerous predators and parasitoids that attack and kill fall webworm. Larvae are getting ready to pupate so it is getting to late for control measures. If using a chemical control, contact is difficult because caterpillars are inside the webbed terminals.

Snowy Tree CricketsSteve Sullivan, The Brickman Group, sent in a photo of tree cricket damage on Euonymus alatus. Tree crickets skeletonize the upper surface of plants including euonymus, cherry laurel, azalea, and rhododendron foliage in August through early October. They feed at night and are rarely found during the day. Unless the tree crickets are significantly damaging the plant, control is not necessary.

Fun Photo of the WeekSteve Sullivan also sent in a photo of a tree frog well camoflauged on a tree trunk. More information is available from MD Department of Natural Resources at:http://www.dnr.state.md.us/wildlife/Plants_Wildlife/herps/Anura/GrayTreeFrog.asp

Tree frogPhoto: Steve Sullivan, The Brickman Group

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Beneficial of the Week, Paula ShrewsburyWasps flying over the turf: What are they? Will they sting me?

One of the general processes of biology is that the more abundant food resources are then the populations of organisms that eat that resource respond positively. Last year (2012) and this year we have seen “higher than average” abundance of white grubs. So it is not surprising we are seeing quite a bit of natural enemy activity. In the August 2nd IPM Alert I discussed Tiphia wasps which are predators of Japanese beetle grubs in the spring (Tiphia vernalis) and masked chafer grubs active at this time of year (Tiphia pygidialis). This week several people have commented on the abundant number of wasps they have seen flying a foot or so over their turf – and of course the accompanying questions “what are they?” and “will they sting me?”. The wasps are referred to as Scoliid or digger wasps. Scoliid because they are in the family Scoliidae (order Hymenoptera) and digger because they locate white grubs in the soil and “dig” down to parasitize them. Scoliid wasps are not aggressive wasps and it is highly unlikely that one will sting you. Scoliid wasps are considered beneficial because they help to suppress populations of scarab beetle white grubs. There are several species of scoliid wasps. Scolia dubia is the common species active at this time in Maryland. They are ~ ¾” in length, have blue-black wings (2 pairs like most Hymenoptera) and black bodies except the end of the abdomen is reddish brown. There are two distinct yellow spots on the reddish brown segments of their abdomen. The bodies are fairly hairy. Scolia dubia mainly attack grubs of green June beetle and Japanese beetle. These scarab beetles lay eggs in the soil of turf, garden beds, and nursery stock. Scarab eggs hatch and white grubs are active in the root zone into October. Scoliid wasp adults are most abundant and noticeable during August. Adult scoliid wasps feed on the nectar of flowers. Scoliid wasps are seen flying several inches above turf infested with grubs often in a figure eight pattern. This figure eight flight is a courtship dance used to communicate with and attract mates. Once mated the female wasp locates a grub in the soil, and “digs” its way down to the white grub. Once the grub is located she stabs it with a paralyzing sting. Although the grub can barely move, it lives for some time. The female wasp lays an egg on the underside of the grub. She will construct a “cell” around the grub, the egg hatches, and the paralyzed grub provides “fresh” food for the wasp larvae. The wasp larva pupates and passes the winter the body of the grub, and emerges as an adult August. Sounds like a pretty nasty way to go for the grub – but it is part of the circle of life.

The presence of Scoliid wasps indicates that green June beetle or Japanese beetle white grubs are present in the turf and that you should monitor the turf for grub abundance and damage. If no damage is notable, let these beautiful wasps do their thing. Although Scoliid wasps may appear a bit intimidating when first seen over the turf, they are beneficial and can make a significant contribution towards suppressing white grub populations, and ultimately damage to turf.

For more information on Scoliid wasps go to:http://www.ces.ncsu.edu/depts/ent/notes/O&T/lawn/note12/note12.html

Scoliid wasp adult (Scolia dubia shown here) feed on the nectar of a variety of flowering plants. Photo: Paula Shrewsbury, UMD

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Plant of the Week, Ginny RosenkranzLagerstroemia indica ‘Peppermint Lace’ is an upright single or multi-stemmed crape myrtle that grows in an upright manor 7-12 feet tall and 6-8 feet wide. Because it is a compact semi dwarf cultivar, it doesn’t need trimming to grow as a hedge, but will need some training as a specimen plant. The dark green, almost olive foliage is powdery mildew resistant even in hot and humid climates. The bright deep pink crinkly flowers are edged in white, bloom from summer to late fall and attract hummingbirds and butterflies to the garden. Plants are hardy from USDA zones 7-9 and are drought tolerant. Full sun, moist but well drained soils, neutral pH and a light covering of mulch to maintain moisture will provide the best growing conditions for ‘Peppermint Lace’ crape myrtle. Japanese beetles are the most common pest.

Weed of the Week, Chuck SchusterFatoua villosa, mulberry weed or hairy crabweed, is a summer annual found throughout the south eastern United States. Named because it is similar to mulberry trees when the weed is less than five inches tall and has less than six leaves. Mulberry weed has prominent hairs on the stems and leaves. The leaves are alternate, toothed, indented with prominent veins, a yellow green color and hairy with a basic triangular shape. Leaves are attached to the stem by a medium length petiole. Stems secrete a milky sap when cut and the plant has an oily odor. Flowers are produced quickly on this plant, often on the very young plant and are tan in color. It produces seed clusters that are pea-sized. The clusters have the ability to discharge the seed up to four feet in from the plant. This weed produces large numbers of seed, so good control from germination on is important. Mulberry weed seeds require sunlight to germinate. Mulberry weed can grow to a height of four feet. The plant prefers moist shaded areas in the landscape or nursery, which is why we are seeing so many this year, easily moving from pot to pot in container nurseries. Seeds can remain viable in the soil or under mulch for several years. Mulberry weed can geminate in a wide range of temperatures, from 60 to 90 °F. Do not compost this weed unless you can determine if the process gets hot enough to really kill weed seeds.

Cultural control can include mulching landscape areas and container plants. Hand removal will work but must start early, as they will produce seed on plants less than three inches in height. Pre-emergent herbicides that have been effective including oryzalin, (Surflan) and isoxaben (Gallery). Post-emergent application of either contact or translocated herbicides is also effective, but once the seed is formed will not prevent seed dispersal. Be cautious with the use of glyphosate products in the nursery or landscape where shallow roots or suckers are exposed.

Mulberry weedPhoto: Carol Kinsley, The Mid-Atlantic Grower

Lagerstroemia indica ‘Peppermint Lace’Photo: Ginny Rosenkranz, UME

Stanton GillExtension Specialist

sgill@umd.edu

Paula Shrewsbury Extension Specialistpshrewsb@umd.edu

Ginny RosenkranzExtension Educatorrosnkrnz@umd.edu

Chuck SchusterExtension Educator

cfs@umd.edu

Karen Rane Plant Pathologistrane@umd.edu

Andrew RistveyExtension Specialistaristvey@umd.edu

David ClementPlant Pathologist

hgic.umd.edu

The information given herein is supplied with the understanding that no discrimination is intended and no endorsement by University of Maryland Extension is implied.

CONTRIBUTORS:

University of Maryland Extension programs are open to all citizens without regard to race, color, gender, disability, religion, age, sexual orientation, marital or parental status, or national origin.

Thank you to the Maryland Arborist Association, the Landscape Contractors Association of MD, D.C. and VA, the Maryland Nursery and Landscape Association, Professional Grounds Management Society, and FALCAN for your

financial support in making these weekly reports possible.

Photos are by Suzanne Klick or Stanton Gill unless stated otherwise.

Upcoming Programs

Greenhouse ConferenceNovember 7, 2013Location: Chesapeake College, Wye Millshttp://extension.umd.edu/ipm

Degree Days (As of Aug 22)Baltimore, MD (BWI) 2787 Dulles Airport 2801 Frostburg, MD 1763 Martinsburg, WV 2586 National Arboretum 3185 Reagan National 3185 Salisbury 3082

To check degree day (DD) accumulations in your local area go to: http://www.weather.com/outdoors/agriculture/growing-degree-days/USMD0100

Note: degree days reported in this newsletter for various pests use the Weather.com web site, a base temperature of 50 °F, a start date of January 1st, and the date of monitoring as the end date.