Extension

While out enjoying the scenery you may see some trees and shrubs covered in webbing. Fall webworms (Hyphantria cunea) are fairly common in Oklahoma and may be especially prominent in the late summer or early fall.
 

Found over most of Canada, the United States and into northern Mexico, fall webworms are present all over Oklahoma, but are more common on the eastern side. They’re greenish-yellow and feature tufts of long, white hairs and have a dark stripe running down their backs. They’re well-known for the distinctive webs they create at the ends of branches.
 
These caterpillars are significant pests by feeding on the foliage of host plants. In Oklahoma, they are particularly fond of persimmon, pecan, black walnut and hickory trees. Damage, for the most part, is caused by the larvae feeding on the leaves and is more aesthetic and not detrimental to the health of the tree. Fortunately, they don’t defoliate the trees, although young pecan and persimmon trees are more susceptible. Lasting damage can occur on pecans as defoliation affects tree vigor, yield and nut quality. The earlier defoliation occurs, the more harmful the damage.
 

Control is rarely warranted for fall webworm since it is usually a nuisance pest. However, control may be necessary to protect pecan yield and tree vigor. There are three main methods of control, including: 

 

Cultural control: 

Larvae and their webs may be cut out of small trees and destroyed, but larger trees with webs present high in the canopy should be treated with insecticide to achieve control.

 

Biological control:

More than 50 species of parasites and 36 species of predator’s attack fall webworm in North America. These natural enemies occur naturally and likely contribute to regulating fall webworm populations in non‐outbreak years.
 

Chemical control:

When using conventional insecticides that rely on contact, sufficient spray pressure is needed to reach and penetrate the webs of these caterpillars. Several insecticides will normally provide control if adequate spray penetrates the webbing. A biorational approach to managing webworms can include the use of Bacillus thuringiensis var. kurstaki, a bacterial insecticide, or products containing an insect growth regulator (tebufenozide, methoxyfenozide) that are specific to caterpillar pests. Either of these latter materials can be applied near the webbing area and the caterpillars will eventually expand their feeding into the treatment zone. However, products containing these insect growth regulators can only be purchased and applied by a licensed pesticide applicator.