Published: April 16, 2013 by the Central Office
EDITORS' NOTE: This is the first of several articles that will be submitted between now and July regarding gypsy moth in Wisconsin. Each highlights a different strategy for managing gypsy moth populations at certain times of year. All of these strategies are effective and some readers may find one more useful than the rest for their situation. Please consider sharing information from all of these releases with your audiences.
MADISON - As spring approaches, state forestry officials urge homeowners to look for signs of gypsy moths. From late April (southern Wisconsin) through May (northern Wisconsin), a new generation of gypsy moth caterpillars will hatch.
"At high numbers, gypsy moth caterpillars are a tremendous nuisance and 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 Bayfield, Marinette and Iowa Counties and a few southeast counties. Individual trees elsewhere may have high populations. Everyone should be on the look-out for gypsy moth because now is the time to act.
Gypsy moth egg mass.
"As soon as possible in April, search for the tan-colored egg masses and destroy any within reach," 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. Before mid-April, oil the egg masses with a horticultural dormant oil labeled for gypsy moth, such as Golden Pest Spray Oil. Avoid using motor oil or axle grease, which can harm the tree. If property owners prefer, they 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 oil before mid-April or drown before hatch."
After oiling or removing all of the egg masses within reach, people can place sticky barrier bands on trees.
"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.
Sticky barrier bands on trees prevent caterpillars from climbing 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 for you. Insecticide treatments are 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."
You can find certified arborists in your area by searching the Wisconsin Arborist Association Web site at [www.waa-isa.org] (exit DNR). Also look in the phone book under "tree service."
Aerial spraying may be an option for property owners with gypsy moth across many wooded acres. For more information on this and other gypsy moth details, visit gypsymoth.wi.gov (exit DNR).
FOR MORE INFORMATION CONTACT: DNR forest health specialists: Bill McNee, southeast Wisconsin, 920-360-0942; Mark Guthmiller, south-central Wisconsin, 608-275-3223; Brian Schwingle, northern Wisconsin, 715-536-0889.