Missouri Ag Connection - Web-Producing Pests on Attack in the Ozarks

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Web-Producing Pests on Attack in the Ozarks
Missouri Ag Connection - 07/22/2016

This is the time of year when you might find your trees and shrubs under attack from the eastern tent caterpillar, a native defoliator, according to Patrick Byers, horticulture specialist, University of Missouri Extension.

Volunteers at the Greene County Master Gardeners hotline have received a lot of calls about the web-producing pests over the last two weeks meaning the pests are already active in the Ozarks.

There are three very common web-producing pests found in Missouri: the fall webworm, the eastern tent caterpillar, and the poplar tentmaker.

Fortunately, control of tent caterpillars is usually simple, and natural predators often curtail outbreaks before they can inflict severe damage according to Byers. However, heavy infestations can weaken a tree by destroying a substantial number of leaves.

Tent caterpillars build their tightly webbed tents in the crotch of various trees and shrubs. Their favorites are fruit trees such as wild cherry, plum, apple, and crabapple, Byers said.

They also feed on ornamental trees such as ash, birch, maple, oak, and poplar. The insects rest during the day within the tent and crawl out at night to chew leaves and developing fruit. As each caterpillar leaves the nest, it will spin a strand of silk as it travels.

"Tent caterpillars overwinter in the shiny brown egg masses glued to twigs. The eggs usually hatch at about the same time as the tree buds begin to break open," Byers said. The emerging larvae will crawl toward the trunk of the tree until they find a suitable site to form a tent.

The fall webworm is often a serious pest of many species of forest, shade, fruit and ornamental trees, except conifers. Trees may be heavily or completely defoliated. Persistent infestations on individual trees may kill branches and top growth.

Under normal conditions, populations of these web-producing caterpillars are kept in check by natural enemies. But occasionally their populations reach a point where artificial control must be employed.

The best nonchemical control for the fall webworm and poplar tentmaker on small to moderate-sized trees is to search the foliage and branches for newly developing web nests or tents, and prune off and destroy the infested leaves or twigs.

Removal of the silken tent of the eastern tent caterpillar cannot be done by pruning because the tents are often found on the fork of a major scaffold limb where pruning would not be desired. However, during the night or on cloudy, overcast days when the caterpillars are in their tents, the tents can be scraped off the trees and destroyed.

For larger shade and ornamental trees, where it is impractical to search and prune out newly developing nests, chemical control is often necessary. Chemical applications should be made as soon as the web nests first appear.

Some insecticides that can provide control are certain formulations of acephate, Bacillus thuringiensis (Bt), imidacloprid, lamda-cyhalothrin, permethrin and cyfluthrin.

MU Extension guide sheet G7271, "Insect Defoliators of Missouri Trees: Web Producers" is available at a local extension office or online at extension.missouri.edu/p/g7271.

For more information, or answers to your specific lawn and garden questions, contact the Master Gardeners of Greene County online at mggreene.org or at 417-874-2963.

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