DNR: Spring time to take action on gypsy moths

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Staff | April 23, 2014

MADISON – With spring here, state forestry officials urge homeowners to look for signs of gypsy moths. From late April in southern Wisconsin through May in northern Wisconsin, a new generation of gypsy moth caterpillars will hatch.

At high numbers, gypsy moth caterpillars can strip trees of their leaves, which puts the tree's health at risk," says Bill McNee, a forest health specialist with the Department of Natural Resources in Plymouth. "The insect's favorite food is oak leaves, but it will feed on many other tree species such as birch, crabapple, aspen and willow," said McNee.

Gypsy moth populations are potentially damaging this year in parts of Ashland, Bayfield and Rock Counties. Individual trees elsewhere may have high populations. Be on the look-out for gypsy moth because now is the time to act.

"As soon as possible in April, search for the tan-colored egg masses," McNee says. Egg masses are about the size of a quarter and are often teardrop shaped.

They can be found on any outdoor surface including trees, houses, firewood piles, play- sets, and other objects. If caterpillars are not hatching from the mass yet, property owners can scrape the masses into a can and drown them in soapy water for at least two days to kill the eggs.

"Do NOT scrape the egg masses onto the ground, step on them, or break them apart. Many of the eggs will still survive and hatch," McNee cautions. "You will have 500 to 1,000 fewer caterpillars for every egg mass you properly drown before hatch."

After removing all of the egg masses within reach, place sticky barrier bands on trees with remaining egg masses.

"These bands will prevent crawling caterpillars from climbing into your trees," says Mark Guthmiller, DNR forest health specialist in Fitchburg.

At a convenient height, wrap a belt of duct tape 4-6 inches wide around each tree trunk, shiny side out. Smear the center of the band with a sticky, horticultural pest barrier available at garden centers. "Routinely sweep the caterpillars gathered under the band from the tree into a bucket of soapy water to kill them," says Guthmiller.

A few weeks after putting up sticky bands place a burlap collection band above each sticky band on trees where caterpillars are still present. This provides a place for larger caterpillars to hide during the day and you can sweep them into a bucket of soapy water each afternoon to reduce the numbers feeding on your trees' leaves. Instructions for burlap bands can be found at: gypsymoth.wi.gov under "tips for protecting yard trees."

After the caterpillars hatch, insecticides can be used to kill them. Insecticides with the active ingredient Bacillus thuringiensis var. kurstaki (Btk) are effective when sprayed on the leaves that small gypsy moth caterpillars eat. Btk is relatively non-toxic and does not persist in the environment. You can spray the leaves of small trees yourself or hire a certified arborist to do a ground-based spray. This is most effective when done in May and early June.

"Spray while the caterpillars are small. If Btk is used, they will die when they eat treated leaves, so they don't become a nuisance or strip all the tree's leaves," McNee says. "Arborists are busy in the spring, so determine whether this is an option for you and then make arrangements soon."

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