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April 3, 2012

caterpillars hatching from gypsy moth egg masses
Caterpillars hatching from gypsy moth egg masses
Photo credit: Bill McNee, DNR

MADISON - Spring is early this year and state forestry health officials say it is already time to battle this year's population of gypsy moths. A new generation of gypsy moth caterpillars has already started hatching in southern Wisconsin, about three weeks early.

"This is the earliest hatching of gypsy moth caterpillars in memory and it is due to the very warm March weather," says Bill McNee, a gypsy moth suppression coordinator with the Department of Natural Resources in Oshkosh.

"This summer we are likely to see the return of nuisance caterpillars in many areas of Wisconsin, and more interest in aerial spraying in 2013 as the populations rebound to high levels," McNee said.

"A wet spring and summer would help to keep the gypsy moth populations down," he said. "Abundant rain favors diseases that kill most of the caterpillars."

At high numbers, gypsy moth caterpillars are a tremendous nuisance and strip trees of their leaves, which may kill the tree. The insect's favorite food is oak leaves, but it will feed on many other tree species such as birch, crabapple, aspen and willow.

What you can do about gypsy moths that are here early

Homeowners are urged to take action to reduce the number of caterpillars that will feed on their trees.

Find egg masses: "As soon as possible in April, search for the tan-colored egg masses," said Mark Guthmiller, another gypsy moth suppression coordinator with DNR for south-central Wisconsin. "Egg masses are about the size of a nickel or a quarter. They can be found on any protected surface including trees, houses, firewood piles, bird houses, and other outdoor objects. Tree trunks and the undersides of branches are common places to find them."

Drown egg masses: Carefully scrape egg masses that you can reach into a coffee can or bucket and drown them in soapy water for at least two days to kill the eggs.

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

Too late to oil: Oiling egg masses with horticultural oil is usually recommended between October and April on days with temperatures above 40 degrees. However, the oil needs to be on the egg mass before caterpillars hatch, so this year it may already be too late for oiling to work well in southern parts of the state.

Use sticky bands: If you find egg masses on your trees, place sticky barrier bands on the trees right away. A demonstration of the technique is available online:

"These bands will prevent crawling caterpillars from climbing into your trees," says Guthmiller. 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. "Each day, sweep the caterpillars below the sticky band into a bucket of soapy water to kill them," says Guthmiller.

Get help to spray: People who have many egg masses on their property and are not in an aerial spray area can hire a certified arborist to protect yard trees after gypsy moth caterpillars hatch. "Spray while the caterpillars are small so they don't become a nuisance or strip the tree's leaves," Guthmiller says. "Arborists are busy in the spring, so find out whether this is an option for you and then make arrangements as soon as you can."

You can find certified arborists in your area by searching the Wisconsin Arborist Association Web site at (exit DNR). Also look in the phone book under 'Tree Service'.

Learn more: More information on the gypsy moth's life stages and options for yard trees and woodlots is available on the Wisconsin gypsy moth website (exit DNR).

FOR MORE INFORMATION CONTACT: Bill McNee, DNR gypsy moth suppression coordinator, northeast and southeast Wisconsin, (920) 303-5421; Colleen Robinson Klug, suppression program public information officer, statewide, (608) 266-2172

Last Revised: Tuesday, April 03, 2012

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