Mosquito season in Trempealeau County, WI: when it starts and ends
Mosquito months in Trempealeau County
In a normal year mosquito season in Trempealeau County, WI starts around April 30 and ends around October 8, about 23 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Trempealeau County, and when
- Start tipping out standing water weekly by April 16.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 8.
- 7 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to July, more so if over 60.
Trempealeau County against the rest of WI
Trempealeau County has the 38th longest season of 72 WI counties, at 161 days against 180 in La Crosse County and 139 in Rusk County. Its mean temperature is 44.9°F.
- Pepin County: April 30 to October 9 (162 days, 1 WNV)
- Waupaca County: April 30 to October 9 (162 days, 0 WNV)
- Wood County: April 30 to October 8 (161 days, 5 WNV)
- Jackson County: April 30 to October 7 (160 days, 0 WNV)
West Nile in Trempealeau County
From 1999 to 2025, CDC ArboNET counted 7 human West Nile cases in Trempealeau County (7 neuroinvasive) across 5 years. The worst was 2025 with 3; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.