Mosquito season in Union County, OR: when it starts and ends
Mosquito months in Union County
In a normal year mosquito season in Union County, OR starts around April 26 and ends around October 12, about 24 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Union 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 12.
- No West Nile cases since 2016, so bites in Union County are a nuisance; check window screens.
Union County against the rest of OR
Union County has the 22nd longest season of 36 OR counties, at 169 days against 225 in Curry County and 95 in Klamath County. Its mean temperature is 49.3°F.
- Clackamas County: April 29 to October 17 (172 days, 1 WNV)
- Gilliam County: April 26 to October 14 (171 days, 0 WNV)
- Sherman County: April 28 to October 14 (169 days, 0 WNV)
- Jefferson County: May 2 to October 12 (163 days, 1 WNV)
West Nile in Union County
From 1999 to 2025, CDC ArboNET counted 8 human West Nile cases in Union County (1 neuroinvasive) across 2 years. The worst was 2007 with 7; the latest was 2007.
See how the dates are worked out, and when mosquitoes go away for the winter.