Forest Tent Caterpillars in Northern Minnesota: BT and Insecticide Options

Northern Minnesota (Chippewa National Forest area): "key hole caterpillars" (forest tent caterpillars with keyhole-shaped spots). Asks about damage and control.

Control Options

• Bacillus thuringiensis (BT)—Dipel/Thuricide; kills caterpillars only; safe for people/pets/wildlife; best on small larvae (<1 inch)
• Insecticidal soaps, spinosad (Conserve), azadirachtin (Azatin)—soft on beneficials
• Carbaryl (Sevin), malathion, acephate (Orthene), permethrin—broader spectrum

Application Tips

• Spray foliage (challenge on large trees)
• Avoid daytime (protect pollinators)
• Orthene for larger caterpillars/heavy feeding (contact action)
• BT must be eaten
• One generation/year—trees releaf after