Mosquito season in Marion County, OR: when it starts and ends
Mosquito months in Marion County
In a normal year mosquito season in Marion County, OR starts around May 10 and ends around October 12, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Marion County, and when
- Start tipping out standing water weekly by April 26.
- Book any yard treatment for early May, ahead of the August peak.
- Repellent can go away after October 12.
- No West Nile cases since 2016, so bites in Marion County are a nuisance; check window screens.
Marion County against the rest of OR
Marion County has the 26th longest season of 36 OR counties, at 155 days against 225 in Curry County and 95 in Klamath County. Its mean temperature is 48.7°F.
- Jefferson County: May 2 to October 12 (163 days, 1 WNV)
- Wheeler County: May 6 to October 11 (158 days, 0 WNV)
- Hood River County: May 11 to October 7 (149 days, 0 WNV)
- Harney County: May 7 to October 1 (147 days, 7 WNV)
West Nile in Marion County
From 1999 to 2025, CDC ArboNET counted 2 human West Nile cases in Marion County (1 neuroinvasive) across 2 years. The worst was 2007 with 1; the latest was 2007.
Background: when the season starts across the US; how the dates are worked out.