Troup extension agent: Caterpillar invasion — Fall webworms

Published 12:00 am Friday, September 2, 2016

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 accidentally 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.

What’s going on in Extension?

• Sept. 1: Planting Food Plots for Deer Wildlife Program. 6:30–8 p.m. at the Oak Hurst Farm, Just south of Jones Crossroads on Ga. Highway 219. Call to register; no cost. Wildlife specialist Dr. Mark McConnell will be the guest speaker.

• Georgia Master Cattleman Program starting Sept. 6. Tuesday evenings from 6:30–8:30 p.m. at the Ag Center. Eight classes. Cost: $75. Call for more information. Still time to sign up.

• Sept. 19: Home Gardening, Food Production and Nutrition Seminar will be held from 9:30 a.m. to 3:15 p.m. at the Chipley Co-op in Pine Mountain. You must pre-register with Harris County Extension at 706-628-4824.

• Market on Main: Every Saturday Morning from 8–10 a.m. Come by and enjoy the pick of the day. Carmike Cinemas LaGrange 10 theater parking lot at East Depot and Main streets.

By Brian Maddy

Contributing columnist

Brian Maddy is the ANR Agent for Troup County Extension. The Troup County Extension office is located at 114 Church St. in LaGrange and may be reached at 706-883-1675, Monday–Friday 8 a.m.–noon and 15 p.m.