UW-Extension Cooperative Extension


Welcome

Welcome to the new UW-Extension gypsy moth website!

Each year, gypsy moth caterpillars defoliate thousands of acres of hardwood forests, yard trees and other urban trees throughout the northeastern United States, including Wisconsin. This site offers tips on how to limit damage to your trees and describes available assistance programs.

The posts below provide management options for homeowners on a month-by-month basis.  Additional information about gypsy moth, including identification, biology, history, and management can be found on the left hand side of the page.  Links to additional websites and publications are also provided.

Photo Credit: Phil Pellitteri UW-Extension.

December – February

Spray or scrape egg masses

Gypsy moth eggs are tough! They can survive temperatures as low as –20°F.

You can spray egg masses with a labelled horticultural oil when the temperature is over 40°F.  Oiling egg masses with horticultural spray oils labeled for gypsy moth (such as Golden Pest Spray Oil) when temperatures are above 40 degrees Fahrenheit will suffocate the eggs so they do not hatch in April.  This can help reduce the population of gypsy moth next spring.  Spray oils labelled for gypsy moth are available for purchasing online or at some garden centers and retailers.  If you have many egg masses, consider adding food coloring to your spray oil so you can see which egg masses you’ve already treated.  Although more difficult, and you must be careful not to damage the bark of the tree, you can also scrape egg masses into a cup and either microwave them on high for 2 minutes or cover them with soapy water for 2 days.  You may then discard eggs in the trash. Don’t leave any part of the egg mass attached and don’t allow it to fall onto the ground, they will survive to hatch next spring!

Spraying gypsy moth egg masses with an approved horticultural oil

Scraping egg masses into a can of soapy water

Photo Credits: Bill McNee WI DNR; Cliff Sadoff Purdue University.

March

Spray or scrape egg masses and watch for treatment program

Gypsy moth eggs are tough! They can survive temperatures as low as –20°F.

You can continue to spray egg masses with Golden Pest Spray Oil when the temperature is over 40°F. The oil kills the eggs, reducing the population of gypsy moth next spring.  This spray oil is available to purchase online or at some garden centers and retailers.  If you have many egg masses, consider adding food coloring to your spray oil so you can see which egg masses you’ve already treated.  Although more difficult, and you must be careful not to damage the bark of the tree, you can also scrape egg masses into a cup and either microwave then on high for 2 minutes or cover them with soapy water for 2 days.  You may then discard eggs in the trash. Don’t leave any part of the egg mass attached and don’t allow it to fall onto the ground, they will survive to hatch next spring!

Treatment areas planned for the state’s Gypsy Moth Suppression Program are posted online in March at: www.gypsymoth.wi.gov.  The yellow and blue Wisconsin map on that webpage shows which counties will be sprayed by the Department of Agriculture, Trade and Consumer Protection and by the Department of Natural Resources.  Treatments start each year in May.

Spraying gypsy moth egg masses with an approved horticultural oil

Photo Credits: Bill McNee WI DNR.

April

Keep caterpillars out of trees using sticky barrier bands

Late April is the time to put up sticky barrier bands around your landscape trees. Immediately after hatching, gypsy moth caterpillars disperse on silk threads and many will fall out of the trees. Barrier bands will prevent caterpillars from returning to the trees and help reduce damage from feeding. View directions to make a sticky barrier band trap using simple household materials. Monitor these each day and sweep caterpillars trapped below the barrier band into a bucket of soapy water.

Two important notes: 1) be aware that trees with deep furrows in the bark allow caterpillars to sneak behind the barrier band and hide.  2) Do not put the sticky material directly on your tree.  Insecticides may also be used to help control gypsy moth at this time of year.

Try using sticky barriers like duct tape and petroleum jelly to trap caterpillars from April into the summer.


Photo Credit: Bill McNee, WI DNR.

May

Caterpillars begin to hatch

Depending on the temperature, gypsy moth caterpillars start hatching in late April through mid-May in Wisconsin. Sticky barrier bands should be up by the first week of May.   Directions on how to make a sticky barrier band.  Monitor these each day and sweep caterpillars trapped below the barrier band into a bucket of soapy water.  Two important notes: 1) be aware that trees with deep furrows in the bark allow caterpillars to sneak behind the barrier band and hide.  2) Do not put the sticky material directly on your tree.  Insecticides may also be used to help control gypsy moth at this time of year.

Aerial spray treatments to suppress outbreaks or slow the spread of gypsy moth occur in mid to late May when caterpillars are very small and vulnerable to the bacterial insecticide Bacillus thuringiensis kurstaki (Btk).  Maps of treatment areas are available online at www.gypsymoth.wi.gov.  Treatment schedules are dependent on weather.  Daily updates are available by phone at: 1-800-642-6684.

Aerial spray treatment to help control gypsy moth caterpillar populations

June

Become a super-predator–put up burlap collection bands

Gypsy moth caterpillars will make their presence known this month! Starting in June, caterpillars will leave the canopy of trees during the day to hide in crevices on the trunks of trees, the sides of buildings and even on outdoor furniture or play equipment. They return to the canopy each evening (or on a very cloudy day) to eat leaves all night.

You can take advantage of this behavior to reduce the number of caterpillars on your landscape trees by putting up burlap collection bands and turning yourself into a super-predator. Caterpillars find the burlap band an attractive hiding spot and will congregate there each afternoon. You can collect the caterpillars from under the bands, scrape them into a cup of soapy water which kills them, or just snip them in half. Directions on how to make a burlap collection band.  For a list of potential burlap suppliers, please visit the links page.

Insecticides may also be used to help control gypsy moth at this time of year.

Photo Credit: Bill McNee, WI DNR

July

Moths emerge at end of month

Gypsy moth caterpillars finish feeding in July. The insects will then pupate and emerge as adult moths in mid-late July.  Male moths look like many other small brown moths but they can be distinguished by the fact that they fly about looking for females in the late afternoon, unlike other moths, which wait until dark. Female gypsy moths are white, 1 1/2 inches long, and although they have wings they do not fly. They are usually found laying an egg mass as in the photo below.  Both the pupa cases and moths can be crushed easily if you can find them.  If you crush a female moth, be sure to use a disposable or washable tool because her pheromone will rub off onto it and attract many male moths.  So do not use your shoe!

Mating disruption is a management technique used to decrease reproduction of the gypsy moth by preventing male moths from finding females.  This technique works by applying the chemical pheromone (attractant) of the female to an area to mask the natural pheromone levels.  As a result, male moths are overwhelmed by the scent and cannot locate females to mate with.  The chemical pheromone used for mating disruption is highly specific to gypsy moth, and is not harmful to humans or other animals.  Two pheromone-based products are currently registered in Wisconsin for mating disruption: Disrupt II (Hercon Environmental) and SPLAT GM (ISCA Technologies).  Both of these products suggest applications approximately two weeks before the emergence of adult moths.  A limitation of this technique is that it is suitable only for low populations of the gypsy moth.

Gypsy Moth Pupae

Gypsy moth adult male (left) and female (right)

Photo Credits: Milan Zubrik, Forest Research Institute – Slovakia, Image 1370017. Forestryimages.org; USDA APHIS PPQ Archive. Image 2652079. ForestryImages.org.

August

Moths lay eggs

Depending on the weather and location, female moths will continue to lay egg masses through the first 2 weeks of August.  Look for egg masses in crevices and protected hiding spots on rough bark, the undersides of branches, under signs attached to trees, and even on buildings, play equipment, benches, and picnic tables.

Beginning the third week of August, look for “pinholes” on the egg masses, evidence that they have been parasitized by a tiny, non-stinging wasp called Ooencyrtus kuvanae. Wait to remove or destroy egg masses until after the first hard frost to allow this beneficial wasp an opportunity to build up its numbers.

Adult female gypsy moth laying eggs on the bark of a tree

Gypsy moth egg mass parasitized by Ooencyrtus kuvanae wasps

Photo Credits: Daniel Herms, The Ohio State University, Image 1523115. Forestryimages.org; MSU.

September

Look for egg masses

If you live in a quarantined county, survey your property for gypsy moth egg masses. Look for egg masses in crevices and protected hiding spots on rough bark, the undersides of branches, under signs attached to trees, and even on buildings, play equipment, benches, and picnic tables.

New egg masses are firm to the touch. Old ones are pale in color, will crush easily, often look tattered and are not of concern. If you find many fresh masses and are interested in participating in the suppression spray program, contact your county suppression coordinator on how to proceed.  Don’t remove egg masses! To qualify for the state sponsored suppression program egg mass densities must meet certain damaging threshold levels on your property. You can conduct predictive surveys on your own.

Hold off treating or removing egg masses until after the first hard frost to let a natural enemy of gypsy moth, Ooencyrtus kuvanae, attack eggs of the gypsy moth.

Examples of a new, fresh egg mass (left) that caterpillars will hatch from next spring and an old egg mass from last year that is already empty (right)

Photo Credit: Bob Queen, WI DNR.

October-November

Sign up now for spray suppression program

Look for egg masses in crevices and protected hiding spots on rough bark, the undersides of branches, under signs attached to trees, and even on buildings, play equipment, benches, and picnic tables.

You can predict whether gypsy moth caterpillars are likely to defoliate your trees next June. This is best done once leaves have fallen. Directions on how to perform a predictive survey are available online at www.gypsymoth.wi.gov.

If you want to participate in the suppression spray next spring, contact your county suppression coordinator now.

When the temperature is above 40°F, spray egg masses with Golden Pest Spray Oil to kill them and reduce the population of gypsy moth next spring.   The spray oil kills the eggs, reducing the population of gypsy moth next spring.  This spray oil is available to purchase online or at some garden centers and retailers.  If you have many egg masses, consider adding food coloring to your spray oil so you can see which egg masses you’ve already treated.  Although more difficult, and you must be careful not to damage the bark of the tree, you can also scrape egg masses into a cup and either microwave then on high for 2 minutes or cover them with soapy water for 2 days.  You may then discard eggs in the trash. Don’t leave any part of the egg mass attached and don’t allow it to fall onto the ground, they will survive to hatch next spring!

Egg masses hidden on the underside of a picnic table

Egg masses on the underside of branches

Photo Credits:  Mark Guthmiller, WI DNR



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