A sign that fall has arrived is the sudden appearance of bug-filled webbing on outer tree branches. Some of these tents can become large, loaded with hundreds of caterpillars.
The fall webworm (also known as a tent caterpillar) is a serious pest of many species of forest, shade, fruit, and ornamental trees (except conifers) found throughout Missouri.
"Trees may be heavily or completely defoliated by tent caterpillars and persistent infestations on individual trees may kill branches and top growth," said Patrick Byers, horticulture specialist, University of Missouri Extension.
Favorite trees for the tent caterpillars include walnut, hickory, persimmon and wild cherry. Although unsightly, damage from the fall webworm is most often inconsequential since trees soon will be losing their leaves anyway.
Beginning in the spring and throughout the early summer, adult tent caterpillars emerge from the ground litter or just below the soil surface where they overwintered as pupae in silken cocoons.
Full-grown caterpillars are about an inch long. They are generally light colored and covered with tiny bumps from which arise tufts of long, light-colored hairs. The head is either orange-red or black.
Eggs are laid in hair-covered masses, each consisting of several hundred eggs, on the undersides of leaves.
Newly hatched larvae immediately begin to spin webbing over the foliage they are feeding upon. As the larvae grow, they enlarge the web nest to enclose more foliage.
Larvae from the same egg mass generally stay together in the nest until the last larval instar (stage). They then leave the nest and feed individually prior to pupating.
"At the end of each generation the webbed nests can be quite large and contain excrement, dried leaf fragments and shed skins of the larvae," said Byers.
During high population densities, small to moderate-sized trees may be completely covered with webbing. It also has been reported that the caterpillars may migrate from one tree to another.
"To control webworms you need to prune them out and destroy small webs," said Byers. "You can also use a labeled insecticide to protect valuable trees."
For more information, contact the lawn and garden helpline operated by the Masters Gardeners of Greene County at (417) 881-8909.
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