Mosquito season in Washington County, IA: when it starts and ends
Mosquito months in Washington County
In a normal year mosquito season in Washington County, IA starts around April 17 and ends around October 19, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Washington County, and when
- Start tipping out standing water weekly by April 3.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 19.
- 1 West Nile case since 2016 (last 2018): you should use repellent at dusk June to August, more so if over 60.
Washington County against the rest of IA
Washington County has the 32nd longest season of 99 IA counties, at 185 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 49.3°F.
- Henry County: April 17 to October 20 (186 days, 2 WNV)
- Shelby County: April 17 to October 19 (185 days, 3 WNV)
- Adams County: April 18 to October 19 (185 days, 2 WNV)
- Clarke County: April 18 to October 20 (185 days, 1 WNV)
West Nile in Washington County
From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Washington County (3 neuroinvasive) across 4 years. The worst was 2018 with 1; the latest was 2018.
Background: when mosquitoes go away for the winter; how the dates are worked out.