Right on schedule, fall webworm infestations are beginning to appear on deciduous trees and shrubs throughout our coastal area. Their large, conspicuous tents are often mistaken for those of the notorious tent caterpillar, which appears in the spring. Although these critters may look awful, they are generally not a threat to our trees and shrubs.
Fall webworms are usually found in groups and feed together on the foliage of their host plant. They are unique from the standpoint that they skeletonize and consume the leaves under the protection of a tent-like web, which they enlarge from time to time as they develop and more food is needed. These webs may cover large portions of a tree.
The caterpillars feed entirely within the tent, which protects them from predators and parasites. The tents also help with mechanical control. When the “tented branches are within reach, they can often simply be snipped off and destroyed.
While the webs and accompanying defoliation caused by fall webworms are unsightly, trees do not die as a result of being defoliated by caterpillar pests. For most gardeners, it’s the unsightliness of the webbing and defoliation that causes the greatest concern.
Out of reach webs can easily be removed by using a hook fashioned from a coat hanger taped to the end of a long pole or a large nail driven through a long pole (exercise appropriate caution around power lines). Destroying the web in this fashion also exposes the caterpillars to predation and parasitism. Yellow jackets, paper wasps, birds, predatory stink bugs and parasitic flies all feed on webworms. Burning webs is not a good idea. Twigs and branches that are defoliated by caterpillars will produce new leaves; twigs and branches killed by fire will not.
Chemical control should be used if the infestation is heavy, or if the tents are high in the trees and difficult to reach. Bacterial insecticides containing Bacillus thuringiensis are formulated specifically to kill feeding caterpillars without harming other insects. Thoroughly cover the leaves next to the nests. As these leaves are incorporated into the nest and eaten, the Bt will be ingested.
Editor’s Note: This article first appeared on www.hometowndebate.com 7/29/12. If you would like to respond to this story, go to hometowndebate.com