Benton County Mosquito Control plans its first spraying for adult mosquitoes from the air on Tuesday.
Spraying from an airplane will begin at sunset and could take two to three hours to complete in Richland, Grandview and Mabton.
In Richland, spraying will be done in the area of Columbia Point and in the east delta where the Yakima River flows into the Columbia River.
In Grandview areas around the Byron Ponds and Grandview Sewage Lagoons will be sprayed. Mabton and nearby Morgan Lake also will be sprayed.
It takes about 20 minutes for the chemical dropped from the airplane to reach the ground, so people who see the plane flying overhead have time to go indoors.
The chemical used, naled, breaks down within hours of application, reducing any long-term effects on the environment, according to the mosquito control district.
The mosquito district said that the unusually hot start to June in the Tri-Cities had brought an early start to the hatch of the type of mosquitoes that can carry West Nile virus.
The district already has used an airplane this year to drop corn cob granules containing a microbe that sickens mosquito larvae into standing water.
Larvicide will be dropped from 6 a.m. to 3 p.m. Tuesday in Grandview, West Richland and Richland.