Mosquito season in Yakima County, WA: when it starts and ends
Mosquito months in Yakima County
In a normal year mosquito season in Yakima County, WA starts around April 12 and ends around October 17, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Yakima County, and when
- Start tipping out standing water weekly by March 29.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 17.
- 4 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Yakima County against the rest of WA
Yakima County has the 6th longest season of 39 WA counties, at 188 days against 205 in Walla Walla County and 132 in Asotin County. Its mean temperature is 51.4°F.
- Kitsap County: April 15 to October 25 (193 days, 0 WNV)
- Franklin County: April 10 to October 18 (191 days, 1 WNV)
- Grant County: April 12 to October 16 (187 days, 0 WNV)
- Wahkiakum County: April 20 to October 24 (187 days, 0 WNV)
West Nile in Yakima County
From 1999 to 2025, CDC ArboNET counted 31 human West Nile cases in Yakima County (23 neuroinvasive) across 9 years. The worst was 2009 with 21; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.