Spongy Moth Aerial Spraying to Begin in May

MADISON, Wis. – Beginning in May, the Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) will treat areas in three western Wisconsin counties for spongy moth (Lymantria dispar) as a part of the national Slow the Spread of the Spongy Moth 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 pest can include the removal of dead trees and loss of property value in defoliated areas. In addition, spongy moth caterpillars shed their skins as they grow, and these bristly skins can irritate the eyes, skin, and respiratory system of humans.

“Spongy moth spreads easily through movement of egg masses and larvae on firewood, vehicles, and outdoor objects, especially during population outbreaks like those we’ve seen across central and eastern Wisconsin over the last couple of years,” said Michael Falk, Forest Pest Survey and Control Unit Supervisor at DATCP. “Our 2025 treatment plan aims to prevent newly established populations from gaining a foothold in uninfested regions of western Wisconsin and to reduce future negative impact to our timber, nursery, and tourism industries.”

In May and early June, small yellow airplanes will spray Bacillus thuringiensis var. kurstaki (Btk) to treetops in select areas in Buffalo, Grant, and Pepin counties. This naturally occurring soil bacteria kills spongy moth caterpillars feeding on treated canopy foliage. Btk is organic; biodegrades within days of application; and does not harm people, bees, pets, or other animals. People with severe allergies may wish to stay indoors during nearby treatment applications.

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 spraying as early as sunrise, flying just above treetops over treatment sites. Sprays continue until they are complete or as long as weather conditions remain favorable.

The national Slow the Spread of the Spongy Moth program has reduced overall spongy moth spread rates in the United States by 87% over the last 20 years. Although Btk treatments are an important component of this program, delays and uncertainty in federal funding have resulted in DATCP reducing Btk treatment acres in 2025 from five counties to three. In addition to Btk treatments, the department will prioritize other spongy moth control activities that align with projected federal funding availability and timelines.

Receive up-to-date information on treatment plans by signing up for email updates, calling the toll-free Spongy Moth Hotline at (800) 642-MOTH, emailing questions to spongymoth@wisconsin.gov, or following DATCP’s social media.

NOTE: This press release was submitted to Urban Milwaukee and was not written by an Urban Milwaukee writer. While it is believed to be reliable, Urban Milwaukee does not guarantee its accuracy or completeness.