QuestionI have noticed in our area a number of key hole catapillars and forget what damage they can do. I live in Northern Minnesota and in a remote area neighboring the Chipawa National Forest. What can I do about them?
AnswerI assume you are talking about the Forest Tent Caterpillar that has a key hole shape spot on it back. These are fairly easy to control with an insecticide spray.
Homeowners can use chemical controls such as insecticides. Forest tent caterpillars are most easily controlled by insecticides when they are small - usually less than one inch long. One effective insecticide is Bacillus thuringiensis - also referred to as Bt. Bt is sold as Dipel or Thuricide and is made from a bacterium that kills caterpillars (moth and butterfly) but is not harmful to people, wildlife, or pets. Other insecticides available to homeowners that don't harm beneficial insects are insecticidal soaps, spinosad (Conserve), and azadirachtim (Azatin). Additional insecticides include carbaryl (Sevin), malathion, acephate (Orthene) and permethrin. When using any chemical control, avoid spraying during the day when bees and other pollinators may be active. Always read and follow label directions. I would use Orthene if the leaves have been eaten and the caterpillars are fairly large. The Bt will work on smaller caterpillars. The Orthene is a contact insecticide where the Bt will need to be eaten by the caterpillar. Both will need to be sprayed on the foliage which maybe a problem with large trees. Hardwood trees will leaf back out after the caterpillars have completed their life cycle. Forest Tent Caterpillars have only one generation per year so the trees will leaf back out.
