Gypsy Moths in Fairfax County

gypsy moth caterpillarThe gypsy moth, Lymantria dispar, continues to be a serious insect threat to trees and shrubs in the United States. It is originally from the temperate regions of Europe, Asia and North Africa. In 1869, the gypsy moth became established in North America after escaping from a Massachusetts lab.

The caterpillar feeds on leaves of forest, shade, ornamental, fruit trees and shrubs. Gypsy moth caterpillars can defoliate a tree by eating 60-100 percent of the leaves. Hardwood trees such as oak and hickory can be killed by two or more defoliations, but a single defoliation can kill some evergreens. Some of the gypsy moth's favorite host trees are oak, hickory, beech, birch, willow and spruce.

Fairfax County Program

In 1982, the Fairfax County Board of Supervisors responded to the threat of gypsy moth by creating an agency to develop and implement strategies that protect the county's forest resources and shade trees on both private and public lands. The Forest Pest Branch uses the Integrated Pest Management approach to monitor and control this pest, including a variety of biological, mechanical and chemical suppression methods.

When serious infestations are found, the Forest Pest Branch develops a caterpillar suppression program. In the summer and fall, county foresters locate and count gypsy moth egg masses to determine where active infestations are occurring throughout the county. If egg mass density and forest habitat meet the criteria set forth by the Virginia Department of Agriculture, an aerial and/or ground spray suppression program will be initiated for the following spring. Homeowners and residents residing in or near the proposed treatment blocks are notified by mail in advance of the upcoming voluntary spray program. In addition, the Forest Pest Section holds public information sessions in areas where treatment is to take place. The aerial spray is applied by helicopters in May using Bacillus Thuringiensis, a pesticide registered with the U.S. Environmental Protection Agency for use in forested residential areas.

Ground spray
Ground Spray
Aerial spray
Aerial Spray

Gypsy moth egg massYou can help the Forest Pest Branch detect gypsy moth infestations by keeping an eye out for the caterpillars in the spring and searching your property for egg masses later in the year. The female moths will lay their eggs starting in mid-July.  The egg masses are tan colored and can be seen on the trunks and upper branches of trees or in sheltered areas, such as under the eves of houses or in wood piles. Please view the Gypsy Moth in North America Web site for more information or contact the Forest Pest Branch at 703-324-5304, TTY 711, or by e-mail if you find gypsy moth caterpillars on your property.


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