Mosquito season in Dewey County, SD: when it starts and ends
Mosquito months in Dewey County
In a normal year mosquito season in Dewey County, SD starts around April 30 and ends around October 7, about 23 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Dewey 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 7.
- 11 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to August, and check SD spray notices.
Dewey County against the rest of SD
Dewey County has the 37th longest season of 66 SD counties, at 160 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 45.6°F.
- Hyde County: May 2 to October 10 (161 days, 1 WNV)
- Corson County: April 30 to October 7 (160 days, 3 WNV)
- Hanson County: April 30 to October 7 (160 days, 5 WNV)
- Spink County: April 30 to October 7 (160 days, 21 WNV)
West Nile in Dewey County
From 1999 to 2025, CDC ArboNET counted 49 human West Nile cases in Dewey County (19 neuroinvasive) across 15 years. The worst was 2003 with 23; the latest was 2024.
More: how the dates are worked out · reading the West Nile counts.