Gypsy Moth in Wisconsin--Pest Management

Gypsy moth hotline:
1-800-642-MOTH

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Wisconsin Department of Natural Resources

Management guide for homeowners

AUGUST—SEPTEMBER: Watch for pinholes in egg masses.

Pinholes indicate the presence of the tiny parasitic wasp Ooencyrtus kuvanae. These wasps will attack gypsy moth eggs as long as the weather is above freezing.

Credit: B. McNee

MID-OCTOBER—MID-APRIL: Destroy egg masses.

Destroy egg masses by spraying them with a horticultural oil (available at lawn or garden centers) or by scraping them off and killing them. Do not use motor oil. Treating egg masses with oil is preferred if you plan on participating in the suppression spray program as it leaves the egg masses in place to be counted by the programs surveyors. Spray the oil onto the egg mass until it is soaked. If you scrape off egg masses, use a knife to scrape all of the eggs into a jar. Eggs can be killed by microwaving them on high for 2 minutes or by soaking in soapy water for 2 days before discarding them in the trash. Don't just scrape egg masses onto the ground or try to crush them with your shoe as they will survive to hatch next spring.

Credit: B. McNee

Credit: Cliff Sadof

LATE APRIL: Place barrier bands on tree trunks.

Barrier bands will prevent caterpillars from climbing back into trees after ballooning or when they have fallen. Barrier bands can be purchased or made using duct tape or other nonporous material that can be wrapped around a tree trunk and coated with a commercially available sticky material such as TangleFoot®. NEVER put sticky material directly on the tree trunk. On thin-barked trees, tie butcher paper or paper bags around the trunk before using the duct tape. The sticky material may need to be re-applied periodically due to rain and other environmental conditions as well as when the bands are covered with caterpillars.

Credit: Forest Service

Credit: Bob Queen

MAY–JUNE: Apply insecticides.

If you choose to use pesticides to control the caterpillars, they must be applied at this time. There are two options: biological and chemical pesticides. For assistance in applying insecticides, consider contacting a certified arborist.

Biological pesticides. The most common treatment used against gypsy moth is a spray of Bacillus thuringiensis, commonly called Bt. This bacterial insecticide kills caterpillars that eat it within a week of its application. Bt causes the cells of the caterpillar’s stomach lining to rupture. Bt is found naturally in soil and degrades within a week when exposed to sunlight. The variety of Bt used against the gypsy moth only affects caterpillars of moths and butterflies. Bt has no affect on animals, birds, people, or even other insects. It is sold under various labels (Bactur, Dipel, Foray, and Thuricide, to name a few). Bt must be applied to trees in May when caterpillars are less than 1/2-inch long. Timing is critical as Bt is significantly less effective on older caterpillars.

Chemical insecticides. Numerous insecticides are registered against gypsy moth in Wisconsin. Many products are available at your local garden center or nursery. Check the label to make sure gypsy moths are listed. Acephate, carbaryl, and malathion are the most common active ingredients and are available in several formulations. If you elect to use a chemical insecticide, consider the potential impact on beneficial insects and natural enemies such as predators, parasites, and honeybees. ALWAYS read and precisely follow the label directions.

EARLY JUNE: Replace barrier bands with collection bands.

Collection bands can be made from medium-weight dark cloth or burlap approximately 12–18 inches wide and long enough to completely wrap around a tree. Using a piece of cord or twine, fasten the middle of the cloth band to the trunk at chest height. Fold the top half of the cloth down to cover the bottom half. Older caterpillars are attracted to these “skirts” when looking for a place to hide during the day. Remove and destroy the caterpillars each day by scraping them into a bucket of soapy water.

Credit: Bob Queen
Credit: Bob Queen

Credit: Bob Queen