By Steve Tomasko, UW PAT Program Outreach Specialist
The Wisconsin Department of Natural Resources is asking people to help look for and destroy gypsy moth egg masses. Killing or removing masses in the fall prevents large numbers leaf-eating caterpillars from hatching in the spring. 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.
The moths will eat the leaves of dozens of different trees and shrubs, some of their favorites are oak, aspen, willow, apple and crabapple, tamarack, white birch, witch hazel, mountain ash, basswood, and linden. In 2021, gypsy moth populations increased for a second consecutive summer due to weather conditions that allowed more caterpillars to survive and become adult moths.
While there are many ways of controlling the pests, one good way in fall is to search for egg masses and remove and destroy them.
Their egg masses are tan-colored lumps about the size of a nickel or quarter. Each mass contains hundreds of eggs and can be found on trees, buildings and other outdoor objects, firewood piles and birdhouses. Old masses with no viable eggs will appear faded and feel spongy when touched. It’s easiest to find egg masses once leaves have fallen from the trees.
To treat or remove egg masses, spray the masses that are safely within reach with horticultural oil or gently scrape them into a container of soapy water to soak for a few days before discarding in the trash. Don’t use motor oil or other lubricants because these can harm the tree and be a pollutant.
Visit the following websites to learn more about gypsy moth egg mass oiling and removal, physical controls, population survey methods and insecticide applications to high-value host trees. An arborist or forester can also be a good resource for anyone dealing with gypsy moths or other tree and shrub pests.
DNR Gypsy Moth website: https://gypsymoth.wi.gov/
UW-Extension Gypsy Moth website: https://fyi.extension.wisc.edu/gypsymothinwisconsin/
