Mosquito season in Polk County, IA: when it starts and ends
Mosquito months in Polk County
In a normal year mosquito season in Polk County, IA starts around April 14 and ends around October 20, about 27 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Polk County, and when
- Start tipping out standing water weekly by March 31.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 20.
- 25 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check IA spray notices.
Polk County against the rest of IA
Polk County has the 14th longest season of 99 IA counties, at 189 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 50°F.
- Mahaska County: April 15 to October 21 (190 days, 1 WNV)
- Montgomery County: April 15 to October 22 (190 days, 3 WNV)
- Warren County: April 14 to October 21 (189 days, 7 WNV)
- Marion County: April 15 to October 21 (189 days, 5 WNV)
West Nile in Polk County
From 1999 to 2025, CDC ArboNET counted 50 human West Nile cases in Polk County (26 neuroinvasive) across 17 years. The worst was 2018 with 12; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.