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

Mosquito months in Whitman County

In a normal year mosquito season in Whitman County, WA starts around April 26 and ends around October 11, about 24 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 Whitman County, and when

• Start tipping out standing water weekly by April 12.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 11.
• 1 West Nile case since 2016 (last 2016): you should use repellent at dusk July, more so if over 60.

Whitman County against the rest of WA

Whitman County has the 23rd longest season of 39 WA counties, at 168 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 48.8°F.

• Skagit County: April 26 to October 14 (171 days, 0 WNV)
• Garfield County: April 25 to October 12 (169 days, 0 WNV)
• Okanogan County: April 24 to October 8 (167 days, 1 WNV)
• Kittitas County: April 25 to October 9 (167 days, 0 WNV)

West Nile in Whitman County

From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Whitman County (2 neuroinvasive) across 2 years. The worst was 2016 with 1; the latest was 2016.

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