Tuesday, July 29, 2008

Gypsy Moth Defoliation on the Increase

Gypsy moth defoliation in Virginia this year has been estimated at over 112, ooo acres, an increase of 46% from last year. The most heavily impacted area was the GW National Forest in Augusta County extending into southern Rockingham County, which, combined, saw almost 43,000 acres of heavy defoliation. Another heavily impacted area for the third year in a row was northwestern Giles County, where more than 15,000 acres of forest was defoliated, most of that being in the Jefferson National Forest.

Gypsy moths were introduced into the United States via Massachusetts in 1869 and have been slowly spreading southward ever since. The first defoliation in northern Virginia was recorded in 1984 and the moths continue to spread slowly southwestward.

Dry spring weather predominated during 2005-2007, helping populations of gypsy moth to build up. This May, however, it was cool and wet at the right time, which can foster the development of a fungus disease affecting the moth population.

“In some areas, caterpillar mortality from disease appears to be quite high,” say VDOF Forest Health Specialist Dr. Chris Asaro . “The caterpillars die only when they are nearly full grown and most of the defoliation is done, so the disease doesn’t have much of an effect for this year. On the other hand, dead caterpillars mean fewer adult moths will be around this summer to lay eggs. So, next year’s defoliation could be considerably lower.”

Egg mass surveys will be completed in late summer and fall and will give a better idea of what can be expected next year.

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