Wisconsin will begin aerial treatments for spongy moth in eight western counties as a part of the national Slow the Spread program. Residents in the affected areas can expect loud, low-flying planes as early as sunrise on select mornings.
During its caterpillar stage, spongy moth can defoliate many kinds of trees and shrubs, leading to plant stress and potential mortality. Possible financial impacts of this invasive plant pest can include loss of property value in defoliated areas, as well as costs associated with pesticide treatments and removal of dead trees. In addition, spongy moth caterpillars shed their skin often, and these bristly skins can irritate the eyes, skin, and respiratory system of humans.
“Spongy moth egg masses and larvae spread easily on firewood, vehicles, and outdoor objects, especially during population outbreaks like those we saw in central and eastern Wisconsin a couple of years ago,” says Michael Falk, Forest Pest Survey and Control Unit Supervisor at DATCP. “Our 2026 treatment plan aims to prevent newly established populations from gaining a foothold in uninfested regions of western Wisconsin, which will mitigate negative impacts on timber, nursery, and tourism industries.”
In May and early June, small yellow airplanes will spray a naturally occurring soil bacteria, Bacillus thuringiensis var. kurstaki, to treetops in select areas in Dunn, Grant, Lafayette, Pepin, and Trempealeau counties. In June and July, planes will apply female spongy moth pheromone, or mating disruptor, to treetops in select areas in Barron, Buffalo, Dunn, Grant, Lafayette, Pepin, and Washburn counties.
Spongy moth caterpillars cannot digest Btk, so they die soon after they eat the leaves. Mating disruptor releases a pheromone that prevents male moths from finding females, thereby preventing reproduction. Both treatments are organic, biodegradable, and do not harm people, birds, bees, pets, livestock, or other animals.
Treatment timing depends on spongy moth development and favorable weather conditions, so exact treatment dates cannot be predicted far in advance. On treatment days, planes begin as early as sunrise, flying just above treetops over treatment sites. Aerial applications continue until they are complete or as long as weather conditions remain favorable.
