Key Features
- Skeletonized or chewed leaves
- Webbed tents at base branch unions
- Hairy caterpillars with white stripe
Symptoms
Caterpillars form webs or nests in central branch unions of trees. Caterpillars are dark in color with a white stripe on their backs. They defoliate trees in April and May. This early season defoliation is not likely to kill the tree. In early May, large (up to 2") caterpillars can be a nuisance when they wander from trees to look for a site to enter the transition stage to adult called a pupa. Egg masses wrapped around twigs are easily found in winter when leaves are not on trees.
Biology
Egg masses winter on twigs. Eggs hatch soon after crabapple and cherry leaves break out of leaf buds in spring. Caterpillars crawl to a central branch junction in a tree and start to form webs. Caterpillars remain in webs during the day to avoid predation from birds. At night, caterpillars crawl from the mass of webs to feed on leaves. Caterpillars continue feeding until early May when they crawl in large numbers to enter the transition stage called a pupa. Adult moths fly in June, mate and lay eggs on twigs in July.
Management Recommendations
When possible, mechanical control is preferred. Look for egg masses in the winter and remove them. In the spring, you can easily remove the tents containing caterpillars during the day with a gloved hand. Kill the caterpillars by dropping them in a bucket of soapy water. NEVER set fire to a rolled up newspaper to burn tents. It will cook and kill your tree. When many nests are present, or too high to reach, an insecticide will give better control. To kill caterpillars without creating other pest problems (spider mites, scale insects) it is best to use biorational pesticides (spinosad, Bacillus thuringensis, tebufenozide, or neem). Caterpillars may have to feed on treated leaves for 1-2 days to get a lethal dose of these materials. When caterpillars are discovered late in season and extensive damage is present, it may be necessary to spray a rescue material to kill caterpillars quickly. Rescue treatments include Sevin(carbaryl) or a pyrethroid (eg. bifenthrin, cyfluthrin, lambda-cyahalothrin,permethrin). To protect bees do not apply pesticides when trees are flowering.
Effective Pesticides
Active Ingredients include: Bacillus thuringiensis var. Kurstaki, Bifenthrin, Carbaryl, Cyfluthrin, Dinotefuran, Horticultural oil (Paraffinic or superior oil) , Insecticidal soap (Potassium salt of fatty acid), Neem oil, Permethrin, Spinosad
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