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Starting in mid May, Shenandoah National Park will begin an aerial spraying program to suppress exotic gypsy moth caterpillars along the sections of the Skyline Drive corridor. Over the past two years, gypsy moth levels have built to where they have caused considerable forest defoliation along parts of the northern section of Skyline Drive in 2007.
The last time the park employed spraying against gypsy moths was in 1995. In the intervening years, a naturally occurring fungus (Entomaphaga maimaga) has emerged as a control of gypsy moth populations. However, the park has seen dry spring weather over the last two years that has suppressed Entomaphaga fungus populations and has allowed the invasive leaf-eating gypsy moths to build to levels that can cause heavy defoliation. In 2007, the park saw 7,305 acres of forest defoliation. To protect tree health in high visitor-use areas, a total of 2,500 acres will be sprayed this spring along portions of Skyline Drive and in Mathews Arm Campground.
A specialized plane will spray a biological insecticide in six spray blocks from mileposts 16.5 to 28.5. A detailed map showing the six treatment areas is available at the park’s website at http://www.nps.gov/shen . Treatment areas were chosen through an annual fall egg mass survey of the gypsy moth population.
Because park weather conditions are unpredictable, officials do not know the exact dates of the spraying operation. However, spraying will be done in the early morning on two separate days (each spray operation lasting about an hour). Based on current insect development prediction, the first spray window may occur from 5/12 - 5/15 and the second spray window may occur from 5/19 - 5/22 (for a map click here).
The park will be using a naturally occurring bacteria - Bacillus thuringiensis var. kurstaki or Btk - as an insecticide. Btk acts upon the digestive systems of moths and butterflies only. Research has shown that Btk is not harmful to humans, pets, plants or most beneficial insects. The spray will not cause harm to painted surfaces, and residues can be removed with soap and water. Btk is registered with the U.S. Environmental Protection Agency and is sanctioned by the U.S. Department of Agriculture for use against gypsy moths.
The goal of the park’s Gypsy Moth Suppression Program, is to protect sensitive historic areas (e.g. historic overlooks), sensitive natural areas, and to provide visitor safety along Skyline Drive and other developed areas (reducing hazard tree development). It is recognized that these suppression goals will not eliminate gypsy moths from the park at large, but will minimize their impacts in specific infestation areas.
For more information about the treatment program or affected areas, call the park’s Forest Health Manager at (540 999-3291).