Fall Webworms

Are you seeing web structures like this on your tree branches?

Don’t be alarmed, these caterpillars are known as Hyphantria cunea or fall webworms. These webs are not tent caterpillars. Tent Caterpillars appear in the spring and are found on the outside of a much smaller web close to the trunk of a tree. Fall webworms enclose themselves inside their web with their food at the end of a leafy tree branch.

In Oregon, fall webworms are commonly seen in black walnut trees, willows, fruit trees and cottonwoods. Their silky webs are unsightly in the landscape and the fuzzy caterpillars inside are unpleasant to deal with, but they rarely kill a tree.

Control Methods:

Mechanical – On small trees and reachable branches, nests can be cut out and destroyed. Infestations need to removed as soon as you see the web, and before the caterpillars mature to their instar stage when they move outside the web.

Biological– The bacteria Bacillus thuringiensis is effective against fall webworms and therecommendation is to spray the leaves just outside the existing tent so when the caterpillars expand their tent they will feed on the treated leaves and die.

Predators and parasites can be effective in controlling fall webworms. The Grange suggests breaking a hole in the web to allow birds, stink bugs, wasps, and other caterpillars to feed on the webworms. But, the Extension Service cautioned about using a high pressure nozzle to make an opening in the web as this action can disperse caterpillars onto other branches,spreading webworms throughout your trees.

Chemical– If you feel your infestation requires more drastic actions you should consult a pest-control specialist about chemical controls.

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Mail Tribune article:


Oregon State University Extension Service: