More Fall Webworms In Washington and Oregon

Have you noticed large, tent-like webs in the branches of trees in our region? The nests of the insects that inhabit them may be unsightly, but are harmless. 

Fall webworms, which infest a variety of plants, can be easily distinguished from tent caterpillars by the larger size of the nest and their tendency to feed exclusively within the nest. Tent caterpillars, on the other hand, venture outside the nest and are seen in the spring.

Vancouver Urban Forestry wants residents to know it’s uncommon for infested plants to die from fall webworms, according to Charles Ray, the City’s Urban Forester.

“Homeowners are understandably concerned to see their plants infested with these caterpillar masses,” Ray says, “but pesticides are not the answer. In fact, the webbing is so well constructed it can repel pesticide spray. Using pesticides removes the caterpillar’s natural predators and other beneficial insects, setting up a cycle for more infestations.”

Webworm larvae, or caterpillars, spin large webs in the trees, which may enclose entire branches. They then feed on the leaves of the plants they inhabit. Their lives as larvae are usually about six weeks, but the webs remain long after they have left. The adult moth is satiny white, with long, soft hair, and may have brown or black spots on the wings.

We're seeing more webworms in our region this year due to the hot summer weather, which has caused the population to increase.

Ray says despite the aesthetic nuisance of webworms, most plants will survive. Generally, the trees or plants will put out new leaves within the same season or the next. As the webworm’s natural predator populations increase, you can anticipate fewer webworms in the future.

The best management strategy is to let nature take its course. The insects will be gone soon enough. If property owners find the infestation is too unsightly, Ray suggests physically removing the nests by using a broom or stick to pull out everything, then placing into a bucket of soapy water to soak for the day.

Webworm pupa overwinters in leaf litter left at the base of trees. To help reduce or prevent webworms next year, rake and dispose of leaves in yard debris carts. You also can take advantage of free leaf disposal coupons, soon to be available in neighborhood newsletters and through the website at cityofvancouver.us/solidwaste. The coupons allow for free disposal at designated drop-off sites starting Oct. 1st, 2018.

For more information on fall webworms, contact Washington State University Extension Service at 360-397-6060. 

For more information on Vancouver Urban Forestry and what you can do to improve our community's urban forest visit cityofvancouver.us/urbanforestry or call (360) 487-8308.

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