March 31, 2004
OAK LEAF ROLLERS CAN BE CONTROLLEDWriter: Edith A. Chenault, (979) 845-2886,firstname.lastname@example.org
Contact: Dr. Bart Drees, (979) 845-7026,email@example.com
COLLEGE STATION – It's like something out of a science fiction movie. Squirmy, twisting THINGS dangling by silken threads from trees. You can't visit your patio anymore. You feel trapped inside the house. They're absolutely horrid.
Actually, oak leaf rollers are harmless to humans. But the caterpillars can do significant damage to trees if left unchecked – particularly in some parts of Central Texas in March and April, said Dr. Bart Drees, entomologist with Texas Cooperative Extension.
"In early spring many species of caterpillars can defoliate oaks and other trees," Drees said. "The caterpillars feed on the early spring growth and occasionally will eat all of the newly-emerged leaves."
One caterpillar that occurs throughout Texas is the oak leaf roller, he said.
When disturbed oak leaf rollers spin silken threads and dangle from leaves and branches. Other caterpillars that dangle from silk threads include the spring and fall cankerworms, which are often called inchworms, he said.
Oak leaf roller moths lay their eggs on twig tips and leaf buds of several different tree species. The eggs remain on the buds or twigs for about 10 months and begin to hatch in March, Drees said.
Once they hatch, the caterpillars, or larvae, feed on tender new spring growth of the tree. The larvae are creamy white to greenish in color and have dark black or brown head capsules.
"Heavily infested trees will occasionally be defoliated by mid-to-late April, when the fully grown caterpillars form the pupa stage on the tips of twigs, in bark crevices or on weeds and other plants growing near infested trees," he said.
When trees become defoliated during the growing season, they become stressed and are subject to serious damage, he said. Green leaves manufacture the sugar (later converted into other carbohydrates) that allows the tree to grow and thrive, he said.
Because of the density and the number of trees, using insecticides to control the oak leaf roller is not feasible.
"Often the best course of action is to simply do nothing," he said. "Post oak trees have survived in South and Central Texas without human intervention through time, despite periodic pest outbreaks and resulting defoliation."
Caterpillar pest outbreaks are cyclic, rarely occurring year after year, he said.
In residential areas, valuable landscape or orchard trees may need to be protected from caterpillar outbreaks.
"Watch trees closely, especially if they have a history of oak leaf roller infestation, from mid- to late-March," Drees said. "If you observe heavy defoliation, the tree can be sprayed with a registered insecticide containing either carbaryl, such as Sevin, the insecticide that contains Bacillus thuringiensis, or any other insecticide products for the control of caterpillars on ornamental trees and shrubs."
For people, Drees suggests wearing broad-rimmed hats and long-sleeved shirts while outdoors if the oak leaf rollers are numerous enough to be bothersome.
"Knowing that these caterpillars are harmless to people and animals and their occurrence is seasonal may provide some comfort," he said.
More information on the oak leaf roller and related species can be found in a newly-revised and released fact sheet (No. E-206) at the Extension Bookstore Web site at http://tcebookstore.org.