Spongy Moth Aerial Spraying to Begin in May

The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) plans to treat select areas in nine western Wisconsin counties for spongy moth (Lymantria dispar) starting in May. Residents can expect loud, low-flying planes in the affected areas as early as sunrise.

A small yellow plane will be treating for invasive spongy moth caterpillars. These non-native insects defoliate many kinds of trees and plants during their caterpillar stage, causing tree stress and potentially tree death. In an attempt to slow their spread, treatment efforts will be focused in western Wisconsin, where spongy moth populations are limited or beginning to build.

“Spongy moth is well established in the eastern two-thirds of Wisconsin, where it reached record population levels in 2023,” says Michael Falk, Forest Pest Survey and Control Unit Supervisor. “DATCP will use effective and environmentally-sound aerial treatment methods to slow its spread into the relatively uninfested western part of the state, in order to limit its impacts in this region and areas lying further west.”

Damaging impacts of spongy moth feeding include the cost of removing dead trees and potential loss of property value. In addition, caterpillars shed their skins several times as they feed, and these bristly skins can irritate the eyes, skin, and the respiratory system in humans.  

Treatments are expected to begin in Wisconsin in May and end in mid-July. Maps of treatment areas are available at https://smaerialspray.wi.gov. Spraying will begin shortly after caterpillars hatch and depends on favorable weather

conditions – calm winds, with no precipitation and high humidity. Planes may start applying treatments as early as 5 a.m., flying just above treetops over treatment sites, and continue until finished or as long as weather conditions remain favorable. Spraying may last into the late morning or early afternoon.

In May to early June, planes will spray Bacillus thuringiensis var. kurstaki (Btk), targeting spongy moth caterpillars. Btk is a naturally-occurring soil bacteria that kills spongy moth caterpillars feeding on treated canopy foliage. Btk is not toxic to people, bees, pets, or other animals. Some people with severe allergies may wish to stay indoors during nearby treatment applications. Btk is used in certified organic food production. The following counties are scheduled to receive Btk treatments: Barron, Buffalo, Chippewa, Crawford, Dunn, Grant, Iowa, Lafayette, and Rusk.

In late June to mid-July, planes will spray an organic, biodegradable mating disruptor containing spongy moth pheromone. Pheromone treatments target adult male moths by inhibiting their ability to locate female moths. The following counties are scheduled to receive mating disruptor: Dunn, Grant, and Lafayette.

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