Hardwoods Plagued by Leaf-Chewing Caterpillars
Pests Build Tents, Webs Along Branch Tips and in Tree Crotches
Jun 18, 2009
Oak, cherry and smaller landscape trees have been plagued with seasonal outbreaks from gypsy moth caterpillars, forest tent caterpillars and eastern tent caterpillars. In most cases, trees will survive if they are healthy and defoliation is not excessive.
Outbreaks Widespread
Gypsy moth caterpillars are voracious feeders and of particular nuisance to oaks, poplars and birch trees, said David Smitley, an entomologist at Michigan State University. Gypsy moth outbreaks tend to be localized and usually last one to three years, Smitley said. The caterpillar is identified by blue/red dots on its back.
Forest tent caterpillars started showing up in late May. It feeds on leaves of many trees, particularly aspen, birch and basswood. The forest tent caterpillar has a brownish body with a row of footprint-shaped white spots along the back.
“Larvae of this insect periodically build to very high numbers in northern hardwoods, oak and aspen forests and can cause complete defoliation for one or more years,’’ said Roger Mech of the Michigan Department of Natural Resources.
Tent Builders
Eastern tent caterpillars, meanwhile, are most likely responsible for unsightly tents in crotches and forks of trees, notably apple and wild or ornamental cherry trees. It occasionally builds nests on pecan, hawthorns, beech and willow, according to the U.S. Forest Service.
Mature eastern tent caterpillars are black, about two inches long with a white stripe along the middle of its back and a row of pale blue oval spots on each side.
“Eastern tent caterpillars can be an eyesore, but cause little tree damage,’’ Mech said.
Caterpillars Still to Come
The early summer appearance of gypsy moth, forest tent and eastern tent caterpillars may steel nerves for the arrival of fall webworms.
Fall webworms usually build tents near branch tips and in some shrubs. Caterpillars are identified by dense yellow to brown hairs along its body. It is known to feed on more than 100 species of forest and shade trees, notably black walnut, crabapple and cherry.
Dealing with Defoliation
Infestations of leaf-chewing caterpillars are not likely to kill mature trees, Smitley said.
“If less than half of the tree canopy is consumed, it will have a minimal impact on tree health,’’ Smitley said. “More than 50 percent defoliation can be stressful, and more than 80 percent usually results in the tree pushing out a new set of leaves in July.’’
Trees that grow new leaves in mid-summer are placed under greater stress because the tree is expending starch reserves to generate the new growth, Smitley said. Trees completely defoliated two years in a row, especially in summers with below-normal rainfall, face the greatest risk.
If shade trees in your yard are defoliated in late June or early July, water the trees when the soil is dry to help them push-out a new set of leaves. Defoliation in late summer or early fall is not as harmful and rarely causes dieback or tree mortality.
