Cankerworm

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Sep 17, 1999

Fall cankerworm is found throughout the US. Spring cankerworm is found in all of North America.

This worm is also known as the "inchworm". They are striped brown and green worms about 1" long. They may drop from trees on fine silken threads when the branch is jarred. Adults are grayish moths. Eggs of fall cankerworms are brown or grayish and are shaped like flowerpots. They are laid on tree trunks and branches in late fall, after frost. Spring cankerworm eggs are brownish purple and laid in groups beneath the bark in early spring while trees are still dormant.

The larvae of both emerge in spring or early summer to feed for 3-4 weeks.

Symptoms of infestation include skeletonized leaves, causing trees to weaken each year. Not much fruit will mature, and sometimes trees will become defoliated and die. You might see the inchworms hanging from branches on threads.

The most vulnerable plants are apples, pears, cherries, maple, willow, elm, deciduous trees and shrubs, and more.

Preventive measures include Bt in spring and a band of Tanglefoot or other sticky material around the trunk. Prevention is the most effective control for this pest.

Pupae of fall cankerworms lay in the soil before the adult emerges to lay eggs after the frost. A thorough fall cleanup, including tilling the first several inches of soil, may help predators find these pests.

You can use horticultural oil (organic kinds of course). spray trees with heavy oil before leaves emerge in spring. If the tree's surface is covered, overwintering eggs will be suffocated. Later in the season, spray the trees every 2 weeks with Bt beginning at end of blossoming and ending a month later. (That's 3 treatments).

Predators include Chalcid and trichogamma wasps, birds, predatory beetles, stinkbugs, tachinids flies, and predatory mite, Nothrus ovivorus.