Mosquito season in Marshall County, IA: when it starts and ends
Mosquito months in Marshall County
In a normal year mosquito season in Marshall County, IA starts around April 20 and ends around October 16, about 26 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Marshall County, and when
- Start tipping out standing water weekly by April 6.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 16.
- 1 West Nile case since 2016 (last 2020): you should use repellent at dusk July to August, more so if over 60.
Marshall County against the rest of IA
Marshall County has the 48th longest season of 99 IA counties, at 179 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 47.7°F.
- Greene County: April 20 to October 17 (180 days, 2 WNV)
- Monona County: April 20 to October 17 (180 days, 2 WNV)
- Jackson County: April 21 to October 17 (179 days, 0 WNV)
- Madison County: April 20 to October 15 (178 days, 0 WNV)
West Nile in Marshall County
From 1999 to 2025, CDC ArboNET counted 6 human West Nile cases in Marshall County (5 neuroinvasive) across 3 years. The worst was 2002 with 4; the latest was 2020.
More: how the dates are worked out · when mosquitoes go away for the winter.