Eastern tent caterpillar
Some of you may be noticing white masses of webby material in fruit trees such as apple, chokecherry, crabapple, and plum. The webs, or tents, are constructed by the larvae (caterpillar) of eastern tent caterpillar. The caterpillars feed on foliage and if populations are high, can completely defoliate trees.
Caterpillars are hairy with blue, black, and orange markings, and a white stripe down their back. When fully grown, the larvae are two inches long. During warm and sunny weather, the larvae leave their tent to feed on foliage. In the evening, as well as cool or rainy days, larvae return to their protective tent. When fully grown, caterpillars measure about two inches long and begin to search for a protected location to spin a cocoon. Once the cocoon is formed, reddish-brown moths will emerge approximately three weeks later. After mating, female moths will lay egg masses on small tree branches. The eggs overwinter on the branch and will hatch in the spring about the time the tree begins to leaf out.
Established trees that are healthy will tolerate feeding by eastern tent caterpillar. The lost leaves will be replaced but until that happens the trees will appear ragged. Trees that were recently planted or are unhealthy may be injured by feeding and would benefit from some type of protection. An easy control option when only a couple of tents are present in a tree is to pull out the webbing with the caterpillars and place into a pail of soapy water or simply place them on the ground and squish them.
When the insect is too numerous to remove by hand, an insecticide may be used. It is best to apply the insecticide while the caterpillars are outside of their tent feeding on foliage. For optimum results, treat the caterpillars before they are an inch long. Insecticides that contain spinosad, Bacillus thuringiensis, or malathion will control caterpillars. Use insecticides with care. Read the label before you purchase the product and again before you use it. Follow all directions and safety precautions.
If you have questions about eastern tent caterpillars, please contact me at 218-299-7338 or nels1657@umn.edu The University of Minnesota, including the University of Minnesota Extension is an equal opportunity educator and employer.
