The Benton County Mosquito Control District will spray for mosquitoes in parts of Richland and West Richland Thursday evening.
Spraying is to begin after sunset and should take less than two hours.
The spray will be focused on an area a mile or more wide along the Yakima River, including the area along Snively and Twin Bridges roads in West Richland, the delta of the Yakima River and Bateman Island.
It also will cover an area near Leslie Road in south Richland.
The district already has dropped a granular insecticide from a plane into wet areas during the daytime and done fogging with a truck.
Fogging Thursday will be from an airplane.
Mosquitoes carry diseases that can sicken and kill people.
Last year the state had nine confirmed human infections of West Nile virus, one of them a Benton County woman in her 70s who died. The year before a Benton County man in his 80s died from the virus.
The chemical naled will be used for the aerial fogging because it penetrates thick vegetation to kill flying adult mosquitoes.
District officials say the small amount of active ingredient should be well below the amount that would pose a health concern. However, it can cause eye irritation.
If you see the plane, you've got time to get indoors before the spray hits you. It takes 20 minutes for the spray to drift from the plane to the ground.
Learn more at mosquitocontrol.org/adulticiding.
West Nile virus was first detected in Washington in 2006.
The virus is found in birds and can spread to humans and other animals through bites from infected mosquitoes.
There’s no human vaccine. To avoid getting bit, you should drain standing water around your home, stay inside or cover up during dusk and dawn, use approved insect repellent and secure doors and screens, say health officials.
Most people who contract West Nile don’t become sick, but some develop a fever and other symptoms, such as fever and body aches.