Mosquito season in Grundy County, IA: when it starts and ends
Mosquito months in Grundy County
In a normal year mosquito season in Grundy County, IA starts around April 22 and ends around October 15, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Grundy County, and when
- Start tipping out standing water weekly by April 8.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 15.
- 2 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Grundy County against the rest of IA
Grundy County has the 63rd longest season of 99 IA counties, at 176 days against 198 in Des Moines County and 160 in Worth County. Its mean temperature is 47.1°F.
- Buena Vista County: April 22 to October 15 (176 days, 2 WNV)
- Butler County: April 22 to October 15 (176 days, 1 WNV)
- Pocahontas County: April 22 to October 15 (176 days, 2 WNV)
- Crawford County: April 23 to October 16 (176 days, 2 WNV)
West Nile in Grundy County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Grundy County (2 neuroinvasive) across 2 years. The worst was 2025 with 2; the latest was 2025.
See how the dates are worked out, and when the season starts across the US.