Allen Baumgard
David F. James
Randall H. Zondag
Allen Baumgard, Ohio Department of Agriculture; David F. James, Ohio State University Extension-Trumbull County; and Randall H. Zondag, Ohio State University Extension-Lake County
Gypsy moth (Lymantria dispar) is potentially one of the most destructive pests in forests and surrounding plantings in Ohio. Large populations of the larval or caterpillar stage of this pest can completely defoliate trees.
Gypsy moths were introduced into the United States in 1869 to cross with the silkworm. A population escaped from the laboratory and continues to spread across the northeastern states as far west as Ohio, Michigan, and even into Wisconsin. Populations in Ohio continue to build, moving from the northeast counties to the south and west. Populations are also moving into northwest Ohio from Michigan.
Gypsy moth populations tend to build and decline over a seven- to 10-year cycle, depending on the weather and predator populations. In the first few years of the cycle, the pest does little visible damage but adds numbers to its population.
In the latter years of the cycle, populations become large enough to cause total defoliation in certain species before the population collapses. Total defoliation of certain trees over a period of years makes them susceptible to stress pathogens, other insect problems, and environmental problems. Because the defoliation occurs so early in the growing season (May and June), many trees never store enough food reserves to develop in the following years.
The most desired species for gypsy moth feeding include alder, apple, aspen, basswood, birch, boxwood, hawthorn, larch, mountain ash, oak, spruce, sumac, willow, and witch hazel.
In 1995, acreage of defoliated trees in Ohio jumped from 100 acres (in 1994) to 14,401 acres. The harsh winter of 1994 followed by the mild winter of 1995 apparently favored gypsy moth population growth. Major defoliation occurred in Ashtabula, Carroll, Columbiana, Geauga, Jefferson, Lake, Mahoning, Portage, and Trumbull Counties.
The 1995 season was the sixth straight year that acreage treated for gypsy moth by the Ohio Department of Agriculture increased. A total of 7,220 acres were treated for population suppression, and 286 acres were treated for educational purposes in 1995.