Pest management for homeowners

Maintain tree vigor

Healthy trees recover from caterpillar defoliation better than stressed trees. By reducing other stresses, you can avoid invasions by secondary insects and fungi that may actually kill the trees. Maintain the vigor shade trees by properly watering and fertilizing. Avoid soil disturbance and soil compaction around the trees as much as possible.

Remove egg masses

Forest tent caterpillar egg masses are laid in summer on twigs of the trees and shrubs, and stay throughout the winter. Since each egg mass contains up to several hundred caterpillars, you can significantly reduce the number of caterpillars that may hatch the following spring by removing egg masses before they hatch. This method is particularly effective to protect smaller trees and shrubs. Egg masses are sturdy, cylindrical structures that encircle fine twigs. They are ¼ to ¾ inch long, and covered with a glossy brown material that protects the egg contents during cold winters. You may find some old egg masses from last year. They are lighter in color with small cavities where the caterpillars hatched.

A barrier band

You can also place a sticky or slippery band around tree trunks to prevent caterpillars from crawling up to the foliage. Sticky bands can be purchased from garden centers or can be home made using duct tape and a waterproof sticky material such as Tanglefoot or petroleum jelly. Wrap the duct tape tightly around the trunk for at least a few inches in width at chest height. Then apply the sticky material to the surface of the duct tape. Make sure that the sticky material does not directly contact the bark of the tree as the sticky material may disfigure or kill the tree. A barrier band will protect trees only from migrating caterpillars. It will not be effective on caterpillars hatched from egg masses in the tree crown. Sticky material may need to be applied repeatedly as it loses its effectiveness when covered by debris or dead caterpillars. Bands can be taken down around mid-June when most forest tent caterpillars complete feeding.

Barrier band, protecting a tree from migrating caterpillars

Turn off exterior lights

Moths of forest tent caterpillars are attracted to lights. When moths are abundant, turn off exterior lights. This may reduce the number of egg masses laid on nearby trees.

Spraying water

A stiff spray of water may work on smaller trees to dislodge young caterpillars and kill them.

Insecticides

Insecticidal soap can be very effective but must be sprayed on caterpillars, not just on leaves.

In a yard situation, a bacterial insecticide, Btk (Baccilus thuringiensis var. kurstaki) or general use insecticides, such as Malathion or Orthene can be sprayed on trees to kill the caterpillars. Btk is specifically targeted to caterpillars, while other chemical insecticides may also kill beneficial insects, such as honeybees and natural predators of forest tent caterpillars. Btk is degraded by sunlight in a week, if not washed by rain before. A second application may be necessary a week later if the number of caterpillars remains high. Insecticidal soap, Btk and general use insecticides are available at major hardware stores, garden centers and nurseries. Be sure to read the label instructions carefully before application.

Spraying soapy water to kill caterpillars on structures

To remove caterpillars from your picnic table or house, individual caterpillars can be killed by pouring or spraying soapy water on them or simply by placing them in soapy water. Soapy water must soak caterpillars to kill them as their hair can repel small amounts of water. There are no traps available to attract forest tent caterpillars or adult moths that can be installed in your yard.