Thursday, August 7, 2008

Landscape - Fall Webworms are Out

You can see many trees with webs on the tips of branches now across Delaware. The following is some information on fall webworm.

Silky tents made by fall webworm caterpillars are beginning to appear now on the branch tips of walnut, hickory, ash, elm, crabapples and other types of trees. The small yellowish-gray webworm caterpillars hide in the webs during the day. Some trees have actually been defoliated from having a tent on nearly every branch. But in most cases, each tree has three or four tents. They look bad, but cause little harm. Tree health is not affected until more than 50 percent of the foliage is consumed, and even then, the trees usually come back just fine the following spring. Pruning-out infested branches is the best strategy if you can reach them. Spraying the foliage around tents with B.t., Sevin, Orthene, or a pyrethroid insecticide will prevent further feeding injury, but the old tent will remain visible for several months. We have many natural parasites and pathogens of fall webworm that will eventually bring infestations under control. Outbreaks usually last two or three years.

Fall webworm on cherry. Photo from Penn State University.

From the July 25 2008 edition of the Michigan State University Landscape Alert Newsletter.

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