MADISON, Wis. – The Wisconsin Department of Agriculture, Trade and Consumer Protection (DATCP) plans to treat 17 western Wisconsin counties for spongy moth, formerly known as gypsy moth, starting in mid to late May. Residents can expect to see and hear loud, low-flying planes as early as sunrise.

Small, yellow planes will be treating for invasive spongy moth caterpillars. These non-native pests 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 low or beginning to build.

“DATCP will be conducting aerial treatments, which are the most efficient and effective method to delay the impacts associated with spongy moth outbreaks,” says Christopher Foelker, DATCP Spongy Moth Program Manager. “Where this insect is established, it has been a periodic public nuisance and damaging forestry pest.”

The harmful effects of spongy moths include the cost of removing dead trees and potential loss of property value. Caterpillars shed their skins several times as they feed, and these bristly skins can irritate the eyes, skin, and the respiratory system in humans.  

The following counties are scheduled to receive aerial treatments: Barron, Bayfield, Buffalo, Burnett, Chippewa, Crawford, Dunn, Eau Claire, Grant, La Crosse, Lafayette, Pepin, Rusk, Sawyer, Trempealeau, Vernon, and Washburn.

Treatments are expected to begin in southern Wisconsin in early to mid-May and end in northern Wisconsin mid-July. Maps of treatment areas are available at Spraying will begin shortly after caterpillars hatch and depends on favorable weather – calm, 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 mid-May to early June, the 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 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.

In late June to mid-July, planes will spray an organic, biodegradable mating disruptor containing spongy moth pheromone, targeting adult male moths which inhibits the adult male spongy moth’s ability to locate females.

To receive up-to-date information on treatment plans:

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