Mosquito Control District to Resume Aerial Spraying


The West Umatilla Mosquito Control District will be conducting targeted aerial mosquito control spraying with a twin engine airplane after sunset on Tuesday, Sept. 1, weather permitting.

The application will be scheduled for the following day if the weather causes a cancellation. The application is taking place to protect the public against mosquitoes carrying West Nile virus in several areas of Western Umatilla County. A total of about 10,000 acres are in the target area that includes the Diagonal Road area between Edwards Road and the Highway 730 Junction, and portions of the Loop Road area.

Residents in the targeted areas can expect to see low-flying airplanes that will spray Dibrom, an organophosphate-based insecticide, at the rate of 0 .7 ounces per acre. The spray rate is 30 percent below the amount approved for safe application by the U.S. Environmental Protection Agency and would not have adverse effects to ornamental ponds or plant life. Dibrom is an insecticide used throughout the United Stated for mosquito control.

While Dibrom is considered safe with little or no risk of toxicity, the Public Health Department recommends some basic steps the public may take to reduce possible exposure to it:

  • Children and pregnant women should take care to avoid exposure when practical. If possible, remain inside or avoid the area whenever spraying takes place and for about thirty minutes after spraying. That time period will greatly reduce the likelihood of your breathing pesticide in air.
  • Close windows and doors and turn off window air-conditioning units or close their vents to circulate indoor air before spraying begins. Windows and air-conditioner vents can be reopened about 30 minutes after spraying.


The district now has 13 confirmed West Nile virus positive samples and is awaiting word on three more that were collected last Thursday and sent to the Oregon State University Veterinary Diagnostic Laboratory in Corvallis for confirmation. The confirmed positive samples have been collected from the Spearman Road area, the Wanaket Wildlife area, on Country Lane, Loop Road, South Ott Road, in the Power City area, and at the Cold Springs Reservoir.

Residents in the district can expect to see an increase in mosquito control operations for the rest of the mosquito season or until about mid September in areas that continue to have positive samples. Ultra Low Volume applications of insecticides from aircraft and truck mounted sprayers will be used to reduce mosquito populations in areas that are infested. These applications will typically be made after sunset when mosquitoes are most active. All applicators are licensed by the Oregon Department of Agriculture.

West Nile is primarily a disease of humans, bird and horses. Some birds, including magpies, blue jays and crows are especially susceptible. Mosquitoes become infected by feeding on an infected bird and can pass the virus to humans, horses or other hosts when they bite. The public is encouraged to continue to alert district officials when they come across dead birds, so the district can track the spread of the virus.