Thursday, May 1, 2008; VA27

Gypsy moths are back for the second consecutive year, so Fairfax County plans to spray from helicopters this month to combat the caterpillars.

More dry weather for the past two years, county officials think, has contributed to an upsurge of gypsy moths, which can kill trees by defoliating them. A natural caterpillar suppressor, a fungus, is inhibited by dry weather.

Helicopters will spray a naturally occurring insecticide in 46 areas. A listing of the treatment areas is available at any public library or county government center, or by contacting http://www.fairfaxcounty.gov/dpwes/environmental/pests.htm.

The county plans to treat about 3,500 acres this year, down from last year's 4,000.

Spraying depends on weather conditions, so officials do not know the exact days that residents can expect the applications. Once they begin, they typically take from seven to 10 days, or longer depending on the weather. Spraying is generally done in early morning and at dusk but may continue all day if weather permits.

The pesticide the county plans to spray is a naturally occurring bacterium: Bacillus thuringiensis, or Bt. Research has shown that the bacterium does not harm people, pets, plants, beneficial insects such as honeybees or painted surfaces, according to the county. Residue can be removed with soap and water.

For more information, contact the county's Forest Pest Program at 703-324-5304, TTY 711, or http://www.fairfaxcounty.gov/dpwes/environmental/pests.htm.