The invasive spongy moth (formerly known as gypsy moth) is back in high numbers this year as part of its typical 10-year outbreak cycle. Spongy moth is a pest of many deciduous trees, especially oak, crabapple, hawthorn, birch, willow and linden.
The Tree Canopy Collaborative, an initiative of the Dane County Office of Energy and Climate Change has created a educational website resource and a map-based reporting tool where members of the public can enter locations where the insects are being found on the Tree Canopy Spongy Moth webpage .
Spongy moth caterpillars feed on tree leaves and can defoliate, weaken or even kill trees, as well as producing cascades of frass (insect poop) that rain down from the trees, creating an unpleasant situation for homeowners. Exposure to caterpillar hairs, pupal cases and egg masses can cause allergic reactions in people as well.
This year, the drought allowed many more caterpillars to survive nd also caused more stress on trees. The adult moths are now out; day-flying brown males are flittering around in search of females. The white, flightless adult female moths are laying spongy beige-colored egg masses on trunks and branches of affected trees. Females are not very discriminating about where they lay egg masses, so they are often also found on buildings, decks, vehicles, lawn furniture, etc.
Egg masses are one to two inches long and oval or teardrop-shaped. Each can contain up to 1000 eggs. Destroying egg masses is very effective for managing the pest. Two methods are to: scrape-and-submerge or spray with Golden Pest Spray Oil. Scrape egg masses off with a putty knife or similar tool into a bucket of soapy water and submerge them for two days. Golden Pest Spray Oil is a soybean oil-based product that penetrates egg masses and smothers the eggs. Order the product online; you may want to join with neighbors to purchase a case of 5 one-gallon concentrate containers. You can also hire a certified arborist to spray the egg masses over winter as they will not hatch until spring. This is often the best course of action as egg masses are often high up in the trees.
