Mosquito season in Bon Homme County, SD: when it starts and ends

Mosquito months in Bon Homme County

In a normal year mosquito season in Bon Homme County, SD starts around April 24 and ends around October 13, about 25 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Bon Homme County, and when

• Start tipping out standing water weekly by April 10.
• Book any yard treatment for late April, ahead of the July peak.
• Repellent can go away after October 13.
• 14 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to August, and check SD spray notices.

Bon Homme County against the rest of SD

Bon Homme County has the 9th longest season of 66 SD counties, at 172 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 47.3°F.

• Turner County: April 22 to October 13 (174 days, 5 WNV)
• Davison County: April 23 to October 14 (174 days, 14 WNV)
• Minnehaha County: April 24 to October 13 (172 days, 86 WNV)
• Brule County: April 25 to October 14 (171 days, 4 WNV)

West Nile in Bon Homme County

From 1999 to 2025, CDC ArboNET counted 28 human West Nile cases in Bon Homme County (12 neuroinvasive) across 13 years. The worst was 2003 with 7; the latest was 2025.

More: how the dates are worked out · reading the West Nile counts.