Mosquito season in Asotin County, WA: when it starts and ends

Mosquito months in Asotin County

In a normal year mosquito season in Asotin County, WA starts around May 13 and ends around September 22, about 19 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Asotin County, and when

• Start tipping out standing water weekly by April 29.
• Book any yard treatment for mid May, ahead of the August peak.
• Repellent can go away after September 22.
• No West Nile cases since 2016, so bites in Asotin County are a nuisance; check window screens.

Asotin County against the rest of WA

Asotin County has the 39th longest season of 39 WA counties, at 132 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 45.6°F.

• Chelan County: May 11 to September 30 (142 days, 0 WNV)
• Ferry County: May 12 to September 24 (135 days, 0 WNV)

West Nile in Asotin County

CDC ArboNET lists no human West Nile cases for Asotin County from 1999 to 2025.

Background: when mosquitoes go away for the winter; how the dates are worked out.