San Antonio Express News
GARDENING, Etc
Sunday, April 18, 2004

By Nathan Riggs

Area Extension offices, nurseries and other gardening centers have been besieged with telephone calls over the past two weeks concerning all of the brown and green caterpillars dropping from the oak trees. These “worms,” “inchworms,” “monsters,” and other names that shouldn’t be put in print are plaguing homeowners from Austin and the Hill Country south to San Antonio. These worms are not webworms, but rather a couple of little critters called the Oak Leaf Roller and the Spring Cankerworm.

In a recent e-publication from Extension Entomologist, Dr. Bart Drees, the private lives and information on these 2 creatures was described in some detail.

The Oak Leaf Roller (Archips semiferana) hatches in April and feeds on newly emerged oak leaves. Once they finish eating, they may drop from the trees and spin cocoons on plants near the tree or they may spin their cocoon in the tree itself. These cocoons are spun around the end of April. At the beginning of May, the adult moths emerge and lay their eggs on the twigs of oak, hackberry, pecan and walnut trees. These eggs will remain dormant until the leaf buds begin to open the following year.

In some instances, these bungy-jumping caterpillars can cause the landscape to look like something out of “The Twilight Zone” or some other eerie situation.

While most oak trees can withstand a limited amount of leaf loss, repeated defoliation can take a severe toll on the energy reserves of the tree as it is forced to produce extra crops of leaves. If its energy reserves are depleted too far, a tree can become vulnerable to diseases or invasions by wood boring insects.

To control these insects on the tree consider a product that contains Bt, or Bacillus thuringiensis, Bt is a bacteria that produces crystals that are toxic to caterpillars only. Once eaten, these crystals destroy the stomach lining of the caterpillars and they stop eating and soon die. Other products containing carbaryl or products labeled for controlling caterpillars on trees and shrubs should also be considered. Treating the grass under the tree may also reduce the numbers of caterpillars that survive, then mature to the adult stage.

The important thing to remember in this outbreak is that our local oak trees have most certainly endured attacks by these acrobatic inchworms in the past, meaning that they will certainly be able to do so again.

This outbreak will be over in another 2 weeks or so, so patience is at a premium wherever they are occurring.

For more information on these worms, check out the following web links:
http://insects.tamu.edu/extension/publications/E206.pdf OR http://insects.tamu.edu/fromthefield/oak_leafroller.html

Special thanks to Dr. Bart Drees for providing some of the information in today’s article.

This article was written by Nathan Riggs, Extension Agent-IPM/Entomology for Texas Cooperative Extension in Bexar County.