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May 27, 2015
Eastern Tent Caterpillars
Cliff Sadof, Purdue Extension Ornamental Entomology Specialist
It’s official! 2015 is the year of the Eastern Tent Caterpillar for the State of Indiana. Throughout the state people have been reporting the presence of white webs or nests at where branches join in flower fruit trees, like crabapples and even some oaks. On a recent drive from Lafayette to Bloomington, I saw entire rows of black cherry completely defoliated. The last time something like this happened was in 2003. The following year the population was very much diminished.
These distinctive hairy caterpillars are dark in color with a white stripe on their backs. 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 mid to late May when they crawl in large numbers to enter the transition stage called a pupa. I actually noticed a fair amount of wandering caterpillars along the Bloomington Campus during my daughter’s graduation from the “other state university” on May 9. Adult moths will begin to fly in June, mate and lay eggs on twigs in July.
Despite the scope of the defoliation, it is primarily a nuisance problem. This early season defoliation is not likely to kill the tree, so control is really not warranted. However, the wandering caterpillars can really be a nuisance. When possible, mechanical control is preferred. If you can reach the tents during the day you can grab the tent and remove the caterpillars and kill them by dropping them into 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.
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