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

Mosquito months in Lake County

In a normal year mosquito season in Lake County, SD starts around April 27 and ends around October 10, about 24 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 Lake County, and when

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

Lake County against the rest of SD

Lake County has the 18th longest season of 66 SD counties, at 166 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 45°F.

• Aurora County: April 27 to October 11 (167 days, 5 WNV)
• Miner County: April 27 to October 11 (167 days, 5 WNV)
• Haakon County: April 29 to October 11 (165 days, 1 WNV)
• Jerauld County: April 29 to October 10 (165 days, 5 WNV)

West Nile in Lake County

From 1999 to 2025, CDC ArboNET counted 39 human West Nile cases in Lake County (10 neuroinvasive) across 17 years. The worst was 2012 with 6; the latest was 2023.

Background: reading the West Nile counts; how the dates are worked out.