The nests created by webworms (Hyphantria cunea) make an unwelcome sight in late summer and fall. The pests create conspicuous webbing between branches of trees and shrubs. Webworms rarely kill their host plants. At their worst, however, webworms can take out large amounts of foliage. They can also create more than one generation each year -- the longer your summer, the more potential they cause for defoliation. Home remedies can do much to control their populations.
Removing webworm nests is the most effective way to keep both the unsightly webs and the larvae populations within at bay. If you catch webworm nests when they enfold only a leaf or two, brush away or crush the nest without removing any branches. For larger, older nests, cut off the sections of branches holding up the webs. Destroy the nests after you take them down by throwing them away or burning them, if you have a permit. If you can't reach nests in taller trees, target them with a strong hose or power washer.
If webworm nests are a major problem on your property, encouraging a wide variety of birds can help keep webworm populations down. Bird houses and bird feeders of various sizes, placed at different heights near trees, will attract different types of caterpillar-eating birds to your property. Get a variety of birdseed and other favorite avian snacks, such as suet. Birdbaths are also welcomed by the birds, as are nearby berry-producing hedges for them to use for food and shelter.
Luring "Good" Bugs
Beneficial insects of special interest for fighting webworms are trichogramma wasps, paper wasps, yellow jackets and assassin bugs. To attract these and other predator insects, plant flat-topped flowers and flowering herbs near affected trees. Good choices include sweet alyssum (Lobularia maritima, U.S. Department of Agriculture plant hardiness zones 5 to 9) and yarrow (Achillea millefolium, USDA zones 3 to 9), Shallow bowls or dishes filled with water, mulched paths, and hedges are all ways to reduce dusty conditions and provide water to keep these "good" bugs from getting dehydrated. Because wasps are an important webworm predator, delay the destruction of yellow jacket and paper wasp nests whenever possible.
During part of the webworm's life cycle, older larvae, or caterpillars, make their way down the tree to the soil, where they overwinter in the soil, wrapped in a cocoon. One useful way of capturing caterpillars coming and going is to install a sticky tree band around the trunk of the tree, according to Rodale's "Ultimate Encyclopedia of Organic Gardening." For older trees, brush petroleum jelly or another sticky compound directly onto the trunk. Younger, more fragile trees can be wrapped with household plastic wrap, secured with string, and painted with the sticky substance of your choice. Reapply the compound as needed, especially in rainy or unseasonably hot weather.
- The Ohio State University Extension: Fall Webworm Management
- Penn State: College of Agricultural Sciences: Fall Webworm
- Rodale's Ultimate Encyclopedia of Organic Gardening; Fern Marshall Bradley, et al
- Mother Earth News: Trichogramma Wasps
- Dirt Doctor: Webworm Newsletter