Contact(s): Bill McNee, DNR forest health specialist, firstname.lastname@example.org, 920-360-0942
March 26, 2019
MADISON - As winter fades and spring arrives, gypsy moth eggs should start hatching in a few weeks. Property owners are urged to treat or remove egg masses now to help protect high-value trees and reduce future caterpillar populations.
The first step a property owner can take is to look for the egg masses. These are tan-colored lumps about the size of a nickel or quarter and may be found on tree trunks, the underside of branches, buildings, firewood piles and other outdoor objects. Each mass may contain 500 to 1,000 eggs. Statewide populations are currently low, although isolated trees and locations may have high populations.
European gypsy moths were first found in Wisconsin in the mid-1970s in the eastern part of the state. By 1989, they had settled along Wisconsin's eastern shore from Milwaukee to Green Bay. Since then, moths have been found in every county. Gypsy moth caterpillars feed on more than 300 species of deciduous and evergreen trees. Their populations tend to outbreak (surge) in localized areas about every 10 years or so. During outbreaks, they may defoliate entire trees or forests.
If egg masses are found, there are two options to help reduce pest numbers. Horticultural oils that suffocate the eggs can be directly applied to the masses and are most effective when temperatures are above 40 degrees and a return to freezing is not imminent. These oils can be purchased at many garden centers and retail stores. Alternatively, egg masses within reach can be scraped into a can of soapy water and left to soak for a few days before being discarded in the trash.
Insecticide treatments may be appropriate for larger trees that have many egg masses. Some types of treatment are done before eggs hatch and some are done while the caterpillars are small. Property owners looking to hire a business to treat large yard trees this spring should contact them soon. A list of certified arborists is available on the Wisconsin Arborist Association website at waa-isa.org (exit DNR). Additional businesses offering insecticide treatments may be found online or in a phone book. Management of woodlots should be done in consultation with a forester.
Additional information about management options for homeowners, including sticky barrier bands and burlap collection bands, is available at the Wisconsin gypsy moth website: gypsymoth.wi.gov (exit DNR).