Mosquito season in Marion County, IA: when it starts and ends
Mosquito months in Marion County
In a normal year mosquito season in Marion County, IA starts around April 15 and ends around October 21, about 27 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 1.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 21.
- 5 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.
Marion County against the rest of IA
Marion County has the 16th longest season of 99 IA counties, at 189 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 49.9°F.
- Polk County: April 14 to October 20 (189 days, 25 WNV)
- Warren County: April 14 to October 21 (189 days, 7 WNV)
- Monroe County: April 15 to October 21 (189 days, 1 WNV)
- Taylor County: April 15 to October 21 (189 days, 0 WNV)
West Nile in Marion County
From 1999 to 2025, CDC ArboNET counted 9 human West Nile cases in Marion County (4 neuroinvasive) across 6 years. The worst was 2025 with 2; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.