Mosquito season in Lyman County, SD: when it starts and ends
Mosquito months in Lyman County
In a normal year mosquito season in Lyman County, SD starts around May 3 and ends around October 5, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Lyman County, and when
- Start tipping out standing water weekly by April 19.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after October 5.
- 4 West Nile cases since 2016 (last 2023): you should use repellent at dusk July to August, more so if over 60.
Lyman County against the rest of SD
Lyman County has the 59th longest season of 66 SD counties, at 155 days against 179 in Yankton County and 139 in Lawrence County. Its mean temperature is 48.1°F.
- Deuel County: May 3 to October 5 (155 days, 5 WNV)
- Hamlin County: May 3 to October 5 (155 days, 12 WNV)
- Fall River County: May 5 to October 7 (155 days, 1 WNV)
- McPherson County: May 4 to October 3 (152 days, 4 WNV)
West Nile in Lyman County
From 1999 to 2025, CDC ArboNET counted 29 human West Nile cases in Lyman County (7 neuroinvasive) across 10 years. The worst was 2003 with 17; the latest was 2023.
Background: reading the West Nile counts; how the dates are worked out.