Cankerworms are becoming more of an issue in North Carolina and throughout the Eastern half of North America from Texas to Nova Scotia.
An inch-worm caterpillar, Cankerworms will outbreak in large numbers every several years.Outbreaks are more common in the northern regions.The fall cankerworm has four life stages, egg, caterpillar, pupa, adult. The adult male is a small brown moth and the adult female grey, with reduced wings, and unable to fly. At the first cold temperatures in the late fall (late November), the adult moths leave their cocoons in the soil. Female moths crawl up the trunks of trees or any vertical object, looking for the highest point or branches on which to lay eggs. Fall cankerworms emerge in the early spring when leaves just begin to open (around late February) and feed immediately. As a tree’s young leaves and buds are destroyed, plants may respond with new buds and leaves. Cankerworms generally don’t kill trees, but this defoliation can drain a tree of some of its energy and may make it weaker. Feeding may continue well into April and cankerworm larvae can blow or drop to an adjacent branch or tree by silk strands. The “inch worms” measure up to one inch in length and may be light green or dark green. When the caterpillars have completed feeding, they will string down to the ground on a silken thread and burrow into the soil to make a new cocoon.
Under the approval of the NC Department of Agriculture & Consumer Services, the City of Charlotte has sprayed infested areas by air with plane or helicopter. The pesticide of choice has been B.t. (Bacillus thuringiensis) a naturally occuring bacteria that as been used by organic farmers and gardeners for decades. It has no known adverse affects on humans, wildlife, pets, fish or honey bees.
Foliar sprays containing B.t. are done in the spring while the small caterpillars are feeding. They stop eating soon after ingestion and die a few days later. Homeowners can use this same product on small trees, but large trees would require professional spray equipment and some amount of cost. Liquid Sevin (carbaryl) for example, could be sprayed on foliage, but would require applications every five days for several times. It would also harm the beneficial insects and may produce a worse situation in upcoming seasons. Insecticidal soap is extremely safe and has no residual. That means that it will kill only the soft-bodied insects that directly contact the spray. About three sprays per week would be required. Large tree spraying is both expensive and troublesome. Other foliar insecticides might include those containing spinosad, bifenthrin, permethrin, or chlorantraniliprole.
Tree Banding– Tree banding in November and December can be an effective way to block wingless females from crawling to the tops of trees to lay eggs. Traps should be in place about mid-November through all January. A sticky agent such as Tanglefoot™ is applied to a band around the tree, rather than the tree itself to protect the bark. Some stores in the Charlotte area sell tree banding supplies and pretreated bands.
Step 1: Install a strip of batting or insulation around the tree a few feet above ground level and below all limbs.
Step 2: Position a band of tar paper or roofing felt 6-12 inches wide, around the trunk circumference covering the batting. Short staples may be used for this. Do not use nails. Electrical tape might be used for small smooth-barked trees.
Step 3: Apply the Tanglefoot or sticky material in a band several inches wide onto the tar paper. Wear disposable gloves for easy clean up. Bands must remain sticky and clear of excessive debris, and may need to be “refreshed” periodically.
Our thanks to the NC Cooperative Extension for this information.