Mosquito season in Umatilla County, OR: when it starts and ends
Mosquito months in Umatilla County
In a normal year mosquito season in Umatilla County, OR starts around April 14 and ends around October 19, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Umatilla County, and when
- Start tipping out standing water weekly by March 31.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 19.
- No West Nile cases since 2016, so bites in Umatilla County are a nuisance; check window screens.
Umatilla County against the rest of OR
Umatilla County has the 11th longest season of 36 OR counties, at 188 days against 225 in Curry County and 95 in Klamath County. Its mean temperature is 51.9°F.
- Clatsop County: April 22 to November 1 (193 days, 0 WNV)
- Washington County: April 16 to October 24 (191 days, 0 WNV)
- Polk County: April 22 to October 26 (186 days, 0 WNV)
- Morrow County: April 18 to October 20 (185 days, 0 WNV)
West Nile in Umatilla County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Umatilla County (0 neuroinvasive) across 1 year. The worst was 2009 with 1; the latest was 2009.
See how the dates are worked out, and when mosquitoes go away for the winter.