INVASIVE SPECIES TECHNICAL NOTE · Invasive Species Technical Notes for additional information. Contact your local NRCS office about biological control of invasive plants in your

NRCS−Montana−Technical Note−Invasive Species−MT-35 1

United States Department of Agriculture NATURAL RESOURCES CONSERVATION SERVICE

Invasive Species Technical Note No. MT-36 January 2019

INVASIVE SPECIES TECHNICAL NOTE

BIOLOGICAL CONTROL OF INVASIVE PLANTS IN MONTANA

Melissa Maggio, Montana Biocontrol Project Coordinator, Missoula, Montana Monica Pokorny, NRCS Plant Materials Specialist, Bozeman, Montana

Figure 1. Biological control collection field day. (Photo by Montana Biocontrol Project) INTRODUCTION

Invasive plants pose an enormous threat to our economy and environment, decreasing the economic value of land and crops, reducing forage for livestock and wildlife, displacing native plant species, reducing plant diversity, and increasing soil erosion and sedimentation. Biological control of invasive plants (also called biocontrol) is the deliberate use of living organisms to limit the abundance of an invasive plant. Classic biological control reunites host-specific natural enemies from the invasive plant’s native range to the plant’s introduced range. Plant-feeding biocontrol agents are usually insects (beetles, flies, and moths) or pathogens that undergo rigorous host-specificity testing before release as an invasive plant management strategy. Biocontrol is a component of an integrated pest management strategy, is synchronized to its host plant, and typically involves an active human role. A successful biocontrol agent has a high reproductive rate, good host searching ability, and is adapted to varied environmental conditions. Biocontrol agents may attack a plant’s flowers, seeds, roots, foliage, and/or stems, reducing its vigor and reproductive capability, making it vulnerable to secondary infections, and/or killing the plant. For biocontrol to be successful, the user should understand some basic biology about the plant and agent. In general, root feeding agents are effective on perennial plants that spread primarily by roots while flower and seed feeding biocontrol agents are typically used for plants that spread by seed. A major component in a biocontrol program is the introduction and establishment of viable populations of biocontrol agents. Site selection for the release of biocontrol agents is one of the most important choices of a biocontrol program. Factors such as soil, slope, aspect, shade, and moisture can influence establishment. The Montana Biocontrol Project has worked with the Montana Natural Heritage Program to develop predicted suitable habitat models to provide insight into site characteristics associated with successful establishment. These models guide the release of agents to sites with suitable habitat where

http://fieldguide.mt.gov/displayOrders.aspx?class=Insecta

NRCS−Montana−Technical Note−Invasive Species−MT-35 2

they are more likely to reduce the invasive plant infestation and build their populations for collecting and moving to new locations.

Implementing a successful biocontrol project includes: • Setting clear goals and objectives for invasive plant management using biocontrol. • Developing a map with invasive plant infestation locations and desired biocontrol release sites. • Acquiring agents through collection or purchase (see vendor list at mtbiocontrol.org). Biocontrol

agents can be collected from sites where they have successfully established. • Storing agents prior to release. Insects can be kept in breathable containers in the refrigerator for

up to three days. In the field and during transport, place breathable containers in a cooler with ice packs and take measures to prevent insects from freezing.

• Releasing of agents and documenting the release date, kind and number of agents, release location, and pre-release conditions of the invasive plant infestation. Anecdotal experience suggests releasing agents at approximately three sites per five-acre infestation, or every quarter-mile for linear infestations. Releasing agents for three consecutive years may increase the likelihood of population establishment.

• Monitoring changes to the plant community and the survival of the biocontrol agent. Document and photograph the timing and frequency of monitoring, location, plant condition (canopy cover, density, injury form agent), presence and density of the agent, and other site management strategies applied to the site (herbicide application, grazing, etc.).

The information below is a general guide for biocontrol agents commonly used in Montana. Contact the Montana Biological Control Coordination Project or reference Montana NRCS Invasive Species Technical Notes for more information.

• Toadflax: Dalmatian and Yellow Toadflax Stem Weevils

• Leafy Spurge: Red-Headed Leafy Spurge Stem Boring Beetle

• Leafy Spurge: Flea Beetle • Spotted Knapweed: Knapweed Root

Weevil ADDITIONAL RESOURCES Bourchier, R., R. Hansen, R. Lym, A. Norton, D.

Olson, C. Randall, M. Schwartzlander, and L. Skinner. 2006. USDA Forest Service, FHTET-05-07. 125 p. Available at: https://www.fs.fed.us/foresthealth/technology/pdfs/LeafySpurgeBiocontrols.pdf

Coombs, E., J. Clark, G. Piper, and A. Cofrancesco, Jr. (eds). 2004. Biological Control of Weeds Invasive Plants in the United States. Western Society of Weed Science, USDA-ARS, Oregon State University Press 467 p.

Montana Biological Weed Control Coordination Project website with Resources, Programs, Events and more. Available at: http://www.mtbiocontrol.org/

Montana Natural Heritage Program. 2018.

Biological Control Predicted Suitability Models. Montana Field Guide Species Accounts, Helena, MT.

Pokorny, M. and J. Mangold. 2018. Montana Noxious Weeds. MSU Extension Publications EB 159. Bozeman, MT. 95 p. Available at: https://store.msuextension.org/

Wilson, L., S. Sing, G. Piper, R. Hansen, R. De

Clerck-Floate, D. MacKinnon, and C. Randall. 2005. Biology and Biological Control of Dalmatian and Yellow Toadflax. USDA Forest Service, FHTET-05-13. 116 p. Available at: https://www.fs.fed.us/rm/pubs_other/rmrs_2005_wilson_l001.pdf

Winston, R., C. Randall, R. De Clerck-Floate, A.

McClay, J. Andreas, and M. Schwarzlander. Biological Control of Weeds in the Northwest. USDA Forest Health Technology Enterprise Team and University of Idaho Extension, FHTET-2014-08. 333p. Available at: https://www.ibiocontrol.org/westernweeds.pdf

Winston, R., M. Schwarzlander, C. Randall, and R.

Reardon. 2015. Biology and Biological Control of Knapweeds. USDA Forest Health Technology Enterprise Team and University of Idaho Extension, FHTET-2011-05. 149 p. Available at: http://bugwoodcloud.org/resource/pdf/Knapweeds.pdf

http://www.mtbiocontrol.org/wp-content/uploads/2017/03/Vendors.pdf

http://www.mtbiocontrol.org/


https://www.nrcs.usda.gov/wps/portal/nrcs/mt/technical/ecoscience/invasive/nrcs144p2_056849/


https://www.fs.fed.us/foresthealth/technology/pdfs/LeafySpurgeBiocontrols.pdf

https://www.fs.fed.us/foresthealth/technology/pdfs/LeafySpurgeBiocontrols.pdf


http://fieldguide.mt.gov/displayOrders.aspx?class=Insecta

https://store.msuextension.org/

https://www.fs.fed.us/rm/pubs_other/rmrs_2005_wilson_l001.pdf

https://www.fs.fed.us/rm/pubs_other/rmrs_2005_wilson_l001.pdf

https://www.ibiocontrol.org/westernweeds.pdf

http://bugwoodcloud.org/resource/pdf/Knapweeds.pdf

http://bugwoodcloud.org/resource/pdf/Knapweeds.pdf

More InformationSee the four associated documents listed below for information about biocontrol agents commonly used in Montana. • Dalmatian and Yellow

Toadflax: Stem Weevils• Leafy Spurge: Red-

Headed Leafy SpurgeStem Boring Beetle

• Leafy Spurge: FleaBeetle

• Spotted Knapweed:Knapweed Root Weevil

Contact the Montana Biological Control Coordination Project or reference Montana NRCS Invasive Species Technical Notes for additional information.

Contact your local NRCS office about biological control of invasive plants in your area. https://www.farmers.gov/connect.

Series Authors:Melissa Maggio, Montana

Biocontrol Project Coordinator, Missoula, Montana

Monica Pokorny, NRCS Plant Materials Specialist, Bozeman, Montana

Dalmatian and Yellow Toadflax: Stem WeevilsBiological Control of Invasive Plants in Montana

Toadflax Biology• Dalmatian Toadflax (Linaria dalmatica)• Yellow Toadflax (L. vulgaris)• Perennials• Taproot and horizontal roots• Reproduces by seed and spreading root

system

Insect Biology• Dalmatian Toadflax Stem Weevil (Mecinus

janthiniformis)• Yellow Toadflax Stem Weevil (Mecinus

janthinus)• The insect species is host specific to the

toadflax species.• One generation of insect per year.• Adults emerge from last year’s stems in

early spring.• Females lay eggs in stems.• Larvae feed in tunnels chewed in stems.• Larvae pupate then become adults by late

summer.• Adults overwinter inside the pupal chamber

inside the stem.• All development, from egg to adult, occurs in

the same stem.

Impacts to Toadflax• Adult feeding stunts shoots and suppresses

flowering and seed production.• Larval stem mining impairs water and

nutrient transport causing desiccation andreduces resources stored in the roots.

Collecting• In the spring, tap insects from toadflax stems

into a breathable container, carefully removeall other insects and plant material. It isimportant to not transfer other weed seedsfrom the collection site to the release site.

• Sweep netting is also an option for collectionbut care must be taken because if the stemsbreak while sweeping, the eggs laid on thosestems will not survive.

• Place 100 to 300 weevils per container andclearly mark container with the toadflaxspecies and stem weevil species names.

• Add toadflax foliage (no flowers or seeds) tocontainers for the insects.

• Cover any openings to prevent weevils fromescaping.

• Immediately store (see below).

Collecting Dalmatian toadflax stem weevils in the spring. (Photo by Montana Biocontrol Project)

Collections of stem weevils should be cleaned of other insects and plant parts (seeds). (Photo by Montana Biocontrol Project)







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Storing• In the field and during transport, place

breathable containers in a cooler on top of ice packs. A towel or newspaper should be between the ice packs and weevil containers to prevent the insects from freezing.

• Store the container / insects in a refrigerator. Insects can be kept in breathable containers in the refrigerator at a moderate temperature for up to three days.

Releasing• Release the stem weevil on the same

species of toadflax it was collected on. Insects collected on Dalmatian toadflax are to be released for Dalmatian toadflax; insects collected on yellow toadflax are released on yellow toadflax.

• Release insects in the spring by scattering the insects close together.

• The toadflax infestation should be at least five acres in size.

• Release 100 weevils per site by scattering the insects close together. Have a minimum of 300 insects for a five-acre infestation and add another 100 insects for each additional five acres of infestation (i.e. 22 releases per 100 acres).

• If the infestation is on a hill, release the weevils at the bottom of the hill.

Monitoring• In the spring, sweep or look for adults on

toadflax stems. If there are approximately six weevils per stem, weevils can be collected from the site for redistribution.

• In the summer, break open toadflax stems to look for larval feeding damage (tunnels filled with sawdust), larvae, or pupae.

• In the fall through spring, dissect toadflax stems and examine for adults.

• Take photos, mark and record GPS coordinates for release locations, and collect data on the toadflax population, insect population, plant damage, and more.

• Monitoring forms are available through the Montana Biocontrol Project at mtbiocontrol.org.

Montana

Adult feeding impacts from the Dalmatian toadflax stem weevil. (Photo by Montana Biocontrol Project)

Stem weevil (Mecinus sp.) on a toadflax flower. (Photo by L. Parsons, U of ID, Bugwood.org)

Utah State University, Bugwood.org



Leafy Spurge: Red-Headed Stem Boring BeetleBiological Control of Invasive Plants in Montana

Leafy Spurge Biology• Leafy Spurge (Euphorbia esula) • Perennial• Brown rhizomes with pink buds, extensive

root system• Yellowish-green flowers• Reproduces by seed and spreading root

system

Insect Biology• Red-Headed Leafy Spurge Stem Boring

Beetle (Oberea erythrocephala)• One generation of insects per year.• Adults emerge in early to mid-summer.• Females girdle the stem, chew a hole in the

stem, and then deposit a single egg on the lower part of the stem.

• Larvae mine down the stem into the root crown and lateral roots.

• Larvae overwinter in the root crown.• Larvae pupate into adults in the root crown

in the spring, chew through plant tissue and emerge from the soil.

Impacts to Leafy Spurge• Larval mining kills shoots and reduces root

reserves.• Insect activity thins leafy spurge infestations,

making them more desirable for leafy spurge flea beetles.

Collecting• In the early summer, collect insects by

hand in warm to hot temperatures. Sweep netting can also be used where beetles are abundant. Hand pick the stem borers out of the net or use an insect separator to carefully remove all other insects and plant material. It is important to not transfer other weed seeds from the collection site to the release site.

• Place 50 to 100 stem boring beetles per breathable container.

• Add leafy spurge foliage (no flowers or seeds) to containers.

• Cover any openings to prevent beetles from escaping.



breathable containers in a cooler on top of ice packs. A towel or newspaper should be between the ice packs and beetle containers to prevent the insects from freezing.




Headed Leafy Spurge Stem Boring Beetle

• Leafy Spurge: Flea Beetle

• Spotted Knapweed: Knapweed Root Weevil






Sweeping for biocontrol agents on leafy spurge. (Photo by Montana Biocontrol Project)









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Releasing• Release insects in the summer by scattering

the insects close together. • The leafy spurge infestation should be at

least five acres in size.• Release 50 stem boring beetles per site.

Have a minimum of 150 insects for a five-acre infestation and add another 50 insects for each additional five acres of infestation (i.e. 22 releases per 100 acres).

• This biocontrol agent works best when used in combination with other leafy spurge agents.

Monitoring• In early spring and summer, dissect roots,

root crowns, and stems looking for larvae.• Sweep net or visually inspecting plants

mid-spring to mid-summer for adults. Search during warm to hot temperatures.

• Take photos, mark and record GPS coordinates for release locations, and collect data on leafy spurge population, insect population, plant damage, and more.


Montana

Adult stem boring beetles on leafy spurge in the spring. (Photo by Montana Biocontrol Project)

Leafy spurge stem boring beetle larva. (Photo by N. Rees, USDQA-ARS, Bugwood.org)

Leafy spurge stem boring beetle adult. (Photo by N. Rees, USDQA-ARS, Bugwood.org)













Leafy Spurge: Flea BeetleBiological Control of Invasive Plants in Montana

Leafy Spurge Biology• Leafy Spurge (Euphorbia esula) • Perennial• Brown rhizomes with pink buds, extensive

root system• Yellowish-green flowers• Reproduces by seed and spreading root

system

Insect Biology• Leafy Spurge Flea Beetle (Aphthona spp.)• One generation of insect per year.• Larvae pupate in the soil in the spring.• Adults emerge from the soil in early summer.• Adults are active during the summer as leafy

spurge bolts, flowers and matures.• Females lay numerous eggs in groups on

leafy spurge stems at or just below the soil surface.

• Larvae burrow into the soil to feed on roots.• Larvae overwinter in the soil.

Impacts to Leafy Spurge• Adults feed on leaves and flowers which

reduces the resources leafy spurge can make and store.

• Adults in high quantities can defoliate plants.• Larval feeding on root hairs and young roots

causes the most damage to the plant by inhibiting root function and stunting stem growth.

Collecting• Sweep net stands of leafy spurge where

flea beetles are abundant. Empty contents of the net into an insect separator to carefully remove all other insects and plant material from the collection. It is important to not transfer other weed seeds from the collection site to the release site.

• Place 500 to 2500 flea beetles per breathable container.

• Add leafy spurge foliage (no flowers or seeds) to containers.

• Cover any openings to prevent flea beetles from escaping.





Sweep netting for leafy spurge flea beetles in the summer. (Photo by Montana Biocontrol Project)

Leafy spurge flea beetles can be copper or black in color. (Photo by USDA-ARS, Bugwood.org)









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Montana

MT-2019 • January 2019

Releasing• Release insects in the summer by scattering

the insects close together. • Select a release site that is not susceptible

to flooding and has sunlight reaching the ground.

• Avoid releasing near ant hills. • The leafy spurge infestation should be at

least five acres in size.• Release 500 flea beetles per site with a

minimum of 1,000 insects for a five-acre infestation. Add another 500 insects for each additional five acres of infestation (i.e. 21 releases per 100 acres).

• This biocontrol agent works best when used in combination with other leafy spurge agents.

Monitoring• In an infestation, look for areas lacking leafy

spurge. These areas may have established biocontrol populations.

• Use a sweep net or visually inspect plants for adults in early to late summer when temperatures are warm to hot.

• Take photos, mark and record GPS coordinates for release locations, and collect data on leafy spurge population, insect population, plant damage, and more.


An insect separator can be used to remove all other insects and plant material from the collection. (Photo by Montana Biocontrol Project)

Adult black flea beetles feeding on leafy spurge. (Photo by Montana Biocontrol Project)

Adult brown flea beetles feeding on leafy spurge. (Photo by Montana Biocontrol Project)



Spotted Knapweed: Knapweed Root WeevilBiological Control of Invasive Plants in Montana

Spotted Knapweed Biology• Spotted Knapweed (Centaurea stoebe)• Biennial or short-lived perennial• Taproot• One pinkish-purple flower head on each

branch• Reproduces by seed

Insect Biology• Knapweed Root Weevil (Cyphocleonus

achates)• One generation of insect per year.• Adults emerge in late summer to early fall,

spending most of their lives below the soil surface on the root crown.

• On hot sunny days, the root weevils climb to the top of the knapweed plant.

• Females lay 100+ eggs on the root crown below the soil surface.

• Larvae hatch in 10 to 12 days and mine into the center of the root.

• Larvae overwinter in the root.• Larvae pupate into adults in the root in the

early summer then chew through the root to crawl to the root crown and soil surface.

Impacts to Spotted Knapweed• Small plants can be killed by larval feeding.• Most damage is done when multiple larvae

occupy a root, reducing plant biomass and the density of the knapweed infestation.

• Tunneling / mining in the root makes the plant vulnerable to bacterial and fungal infections.

Collecting• Hand pick the root weevils off the top of

knapweed plants on hot, sunny days or from under basal leaves during cooler temperatures. Carefully remove all other insects and plant material from the collection. It is important to not transfer other weed seeds from the collection site to the release site.

• Place 50 to 200 root weevils per breathable container.

• Add spotted knapweed foliage (no flowers or seeds) to containers.

• Cover any openings to prevent root weevils from escaping.















A collection of root weevils in a breathable container with knapweed foliage for the insects. (Photo by Montana Biocontrol Project)









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Montana

MT-2019 • January 2019

Releasing• Release root weevils in the summer by

scattering the insects close together. • The spotted knapweed infestation should be

at least five acres in size.• Release 100 root weevils per site with a

minimum of 300 insects for a five-acre infestation. Add another 100 insects for each additional five acres of infestation (i.e. 22 releases per 100 acres).

• Release on a hot, dry, well-drained site with dense patches of spotted knapweed.

• Release early in the morning or late in the evening when temperatures are relatively cool.

• This biocontrol agent works best used in combination with other spotted knapweed agents. In general, the knapweed flower weevil (Larinus spp.), knapweed seedhead fly (Urphora spp.), and knapweed moth (Agapeta zoegana) are already well distributed in Montana.

Monitoring• Pull spotted knapweed plants to inspect

roots for damage.• Look for larvae, pupae, or adults in the roots

in spring to late summer.• Use a sweep net or visually inspect plants

for adults in late summer to early fall when temperatures are warm to hot.

• Take photos, mark and record GPS coordinates for release locations, and collect data on spotted knapweed population, insect population, plant damage, and more.


The root weevil climbs to the top of the knapweed plant on hot, sunny days. (Photo by Montana Biocontrol Project)

Knapweed root weevil larva mining in the root. (Photo by C. Minteer, U of AR, Bugwood.org)



Documents

INVASIVE SPECIES TECHNICAL NOTE · Invasive Species Technical Notes for additional information. Contact your local NRCS office about biological control of invasive plants in your