Caterpillar Invasion: Fall Webworms

Published 11:39 pm Friday, August 18, 2017

By Brian Maddy
Brian Maddy is the ANR Agent for Troup County Extension. The Troup County Extension office is located at 114 Church Street, LaGrange, GA. 30240 (706) 883-1675. Monday – Friday/8 a.m. to noon and from 1 to 5 p.m. Email:

Fall seems to be the time of the year when moths invade our landscape. Their progeny will munch and crunch on many of our landscape plants. You may have noticed web sacks hanging in trees along the roadways of Troup County. These are the homes of the fall webworms. They are usually at the end of branches rather than in the crotch of trees like the spring tent caterpillars.

Fall webworms are native to North America, Japan and Korea. In 1946, they were introduced into Europe accidently and are considered a major invasive species. They can feed on over 600 species of trees and shrubs but prefer pecans, sourwoods, persimmons, oaks and apples.  You most likely will see them in pecan trees.

The pupae overwinter in mulch, leaf litter and the soil in cocoons. A white moth, some have small black spots on them, emerge in the spring during evening hours. After mating, the female will lay up to 900 eggs on the underside of a leaf.

Seven days later they hatch into worms that may either have black heads and yellowish-white bodies or red heads with brown bodies. Both are covered with long, soft gray hairs.

They feed in large groups in the sacks which protect them from birds and predatory wasps. The tiny webworms leave only the veins in the leaves as they feed. As they get larger they will consume the whole leaf. They molt six times and the bag expands to contain all the shed skins, droppings and dead leaves. It becomes a mess.

They can envelope a small apple tree easily. After four weeks of feeding they drop down, spin cocoons, pupate and the process begins again. Georgia can have up to four generations of fall webworms.

Most of the damage is cosmetic. Healthy trees can withstand insect damage to a great degree without lasting effects. However, weak trees may be damage or killed. Fall webworms usually attack in mid to late summer and the tree has already had a chance to store food.

If the webs are within reach of a pole or stick, you can knock them down where birds and wasps will make quick work of them.

Do not do this near power lines. Spraying is not generally required unless the webs are on a young tree and webs are within reach.

The entire tree must be treated and the spray must penetrate the web. Trombone sprayers or a power sprayer may have to be used. You may have to hire professional arborist or landscaper to do this.

If you do spray you may use insecticidal soap, horticulture oils or Bacillus thuringiensis (Bt) to kill small caterpillars. They are less likely to kill beneficial natural predators. If the caterpillars are large you may have to use products such as Sevin, bifenthrin or cyfluthrin. Always follow label directions.

Cutting the limbs where the webs are located may cause more damage to the tree than the worms. Toleration of the fall webworms may be the best bet.

We have moved to 144 Sam Walker Drive. We are next to the sheriff’s office in the last building on the left. Our phones and emails are the same. Stop by and see our new office.

What’s going on in Extension?

Grassmasters Program:  If you are raising forages for sheep, goats, horses or cattle and want to improve your pastures and hay this class may be for you. Begins August 31 and ends October 26. This class will meet on Thursday evenings from 6:30  to 8:30 p.m. for seven evenings. The cost is $25 per family. Call UGA Extension-Harris County to register. (706) 628-4824. This program is sponsored by Troup, Meriwether and Harris County Extension.

Market on Main: Every Saturday at the LaGrange Theater parking lot from 8  to 10 a.m. The freshest produce in Troup County.

August 15: Troup County Cattleman; 7 p.m. at the Ag Center; Levi Russel: Making money in the cattle business. Call ahead for reservations: (706)882-5561 $6 per person

August 17: Lunch-n-Learn at the Lagrange Library: common Pests of Vegetable Plants

August 21:  Beekeepers Meeting; 7 p.m. at the Ag Center; Topic: Native Plants for Pollinators; Guest speaker: Brian Maddy

September 5th: Lunch-N-Learn at the LaGrange Library; noon to 1 p.m. IPM: “All You Need to Know About Houseplants”

August 31: Grassmasters Program; 6:30 to 8:30 p.m. at the Ag Center. Call for reservations.

If you have any questions or concerns, stop by or call the office.