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

Mosquito months in Mellette County

In a normal year mosquito season in Mellette County, SD starts around April 30 and ends around October 10, about 23 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 Mellette 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 10.
• 4 West Nile cases since 2016 (last 2022): you should use repellent at dusk July to August, more so if over 60.

Mellette County against the rest of SD

Mellette County has the 27th longest season of 66 SD counties, at 163 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 48°F.

• Hand County: April 29 to October 9 (163 days, 6 WNV)
• Ziebach County: April 29 to October 9 (163 days, 2 WNV)
• Jackson County: May 1 to October 11 (163 days, 1 WNV)
• Todd County: May 1 to October 11 (163 days, 3 WNV)

West Nile in Mellette County

From 1999 to 2025, CDC ArboNET counted 13 human West Nile cases in Mellette County (4 neuroinvasive) across 9 years. The worst was 2003 with 5; the latest was 2022.

See how the dates are worked out, and reading the West Nile counts.