Spongy Moth Aerial Treatment Update

Treatment is planned in Dunn County on Thursday, May 28 to reduce spread and negative effects of spongy moth (Lymantria dispar)

Spongy moth is an invasive insect that feeds on the leaves of oaks, maples, aspen, apple, birch, and many other species of trees and shrubs. These caterpillars eat so many leaves that the trees and shrubs they feed on are left vulnerable to disease and other environmental stressors. Their allergenic hairs can cause eye, skin, and respiratory irritation when handled or in close contact with humans. Aerial treatment is necessary to slow the spread of spongy moths—and their negative impacts— as they advance westward.

Planes will apply a product called Foray 48B that contains Bacillus thuringiensis var. kurstaki (Btk), a naturally occurring soil bacteria. Spongy moth caterpillars cannot digest Bkt, so they die soon after they eat the leaves. Btk is not toxic to people, bees, pets, or other animals, and is approved for use in certified organic food production. It will break down in sunlight within a few days after application.

Weather permitting, state agencies will be conducting aerial treatments in select areas in Dunn County on Thursday, May 28, 2026.

Treatment will begin as early as sunrise and continue as weather conditions allow or until application is complete. People who have allergies may wish to stay indoors or leave the area until treatment is done. The yellow planes are loud and will fly low, just above the tree canopy, which may frighten pets or livestock. Those with animals may use their discretion to reduce stress by keeping them indoors or monitoring their behavior during aerial treatments.

Maps of treatment areas and spray plan updates are available at smaerialspray.wi.gov. Spray plan updates are also available on social media through Facebook, Instagram, and X; and through pre-recorded messages on the Spongy Moth Hotline at 800-642-6684, option 1.

NOTE: The State of Wisconsin does not offer state-sponsored aerial treatments or a cost sharing program to suppress established populations of spongy moth. To learn more about spongy moth management, visit the Wisconsin Spongy Moth Resource Center at spongymoth.wi.gov.

DATCP media release.