Pecan Tree Webworms

Fall webworms (Hyphantria cunea) are the larvae of fall webworm moths. These insects feed on over 600 different trees and shrubs, but they prefer species such as walnut, ash, mulberry and pecan. They create unsightly webs on the branches, but rarely cause serious damage. Homeowners control webworms through both chemical and cultural methods.

Identification and Life Cycle

Adult fall webworm moths are 1-inch-long moths with white bodies. They lay small, rounded yellow eggs on the lower surfaces of leaves and cover them with white hair to hide them from predators. The eggs hatch into hairy caterpillars. The larvae grow to around 1.5 inches. Their colors vary from pale green to almost black; some have reddish-orange heads, while others have black heads. They spend the winter in a 1/2-inch-long dark, cylindrical pupae surrounded by a silken cocoon and emerge in the spring as adults.

Effects

Webworms build large webs on the ends of pecan tree branches around the end of summer and the beginning of fall. They feed on the leaves within the webbing for several weeks as they prepare to pupate. They will increase the size of their webs if they run out of leaves. Inside the webbing, they strip the leaves down to mid-vein. They rarely cause serious damage, since they do not usually appear in large numbers, and healthy trees are able to withstand large amounts of defoliation. The unsightly webbing remains in the tree long after the insects have pupated.

Similar Species

Several types of tent caterpillars also create webs in trees and are easily confused with fall webworms. Tent caterpillars are around 1.5 inches long with hairy bodies, bright colors and white or yellow markings that vary depending upon the species. Eastern tent caterpillars prefer fruit trees such as apple, cherry and hawthorn. They build their tents between the forks in tree branches during the spring. Sonoran and Forest caterpillars feed on many oaks, as well as other deciduous tree species, while Western tent caterpillars prefer wild plum or oak. Tent caterpillars do not generally prefer pecan trees, but they will attack other species, including pecan, if food is scarce.

Control

Since fall webworms generally do not do serious damage to pecan trees, you can ignore them and eventually they will go away on their own, according to Willie O. Chance from the University of Georgia. If you do decide to spray the tree, you will need to hire a tree service person who can get the insecticide inside the webs. You can also spray the tree with Bacillus thuringiensis, a bacterium that sickens and kills caterpillars, or you can use horticultural oils or insecticidal soaps. If the webs are within reach, you can tear them open or knock them out of the tree with a long stick. This leaves the worms vulnerable to predators.

References

• University of Georgia: Fall Webworms; Willie O. Chance; 2005
• North Carolina State University: Fall Webworm; Stephen Bambara and James R. Baker; 2006
• Texas AgriLife Extension: Fall Webworm
• Cornell University Insect Diagnostic Laboratory: Fall Webworm; Carolyn Klass; January, 2010
• Texas Agricultural Extension Service: Tent Caterpillars; J.A. Jackman; August, 2000