How Wisconsinites Can Help Curb The Spread Of The Invasive Spongy Moth

WISCONSIN — You have probably heard about the spotted lanternfly and the zealous efforts to curb their proliferation across America. Fortunately, their spread has been limited in Wisconsin; But there is another similar and more expansive critter that officials are hoping to curtail early this year.

On Monday, the Wisconsin Department of Natural Resources asked property owners to keep an eye on their trees for signs of spongy moth egg masses. The invasive insects thrive in warm, dry weather, but even average weather this upcoming spring and summer will encourage the further outbreak of them, according to the DNR.

In their caterpillar stage, the spongy moth feeds on foliage which can result in plants losing much of their leaf coverage, according to an entry by the University of Wisconsin-Madison Horticulture Division of Extension. Repeated loss of leaves can weaken trees and make them more susceptible to other diseases or pests, according to the entry.

The spongy moth is already generally established across Wisconsin excluding the western part of the state where state officials are conducting spraying efforts to curb the spread.

The caterpillars will feed on many types of plants, but they prefer to feed on oak, birch, crabapple, aspen, willow and linden trees, according to the DNR.

"To know if spongy moth are on your property, look for egg masses which are tan-colored lumps about the size of a nickel or quarter," said the DNR news release. "These masses are found on trees, buildings and other outdoor objects and may also be found inside protected places such as firewood piles and birdhouses. Egg masses produced in 2022 will feel firm and appear darker in color than older egg masses, which appear faded, feel spongy, and do not contain viable eggs."

One way to destroy the egg masses is by spraying them until soaked with a spongy moth horticulture oil, which can often be found at lawn and garden centers, according to a spongy moth management guide from the University of Wisconsin.

You can also scrape the masses off into a jar and then soak them with soapy water for two days before placing them in the trash, but people should avoid harming a tree's bark and should avoid trying to crush the masses as the eggs could survive until next spring.

When high numbers of egg masses are found on large trees, professional treatment may be needed, the DNR said. Insecticides work best in mid-to-late May and sometimes early June when the caterpillars are small.

Trees that carry the moths may be at a higher risk of dying if they lost a lot of leaves or were stressed by drought in 2022, the DNR said.

You can find more information on the spongy moth online including details about handling egg masses and applying insecticide.