Mosquito season in Mercer County, ND: when it starts and ends
Mosquito months in Mercer County
In a normal year mosquito season in Mercer County, ND starts around May 11 and ends around September 28, about 20 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Mercer County, and when
- Start tipping out standing water weekly by April 27.
- Book any yard treatment for mid May, ahead of the July peak.
- Repellent can go away after September 28.
- 25 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to July, and check ND spray notices.
Mercer County against the rest of ND
Mercer County has the 46th longest season of 53 ND counties, at 140 days against 160 in Sheridan County and 135 in Rolette County. Its mean temperature is 43.1°F.
- Renville County: May 9 to September 28 (142 days, 0 WNV)
- Divide County: May 9 to September 27 (141 days, 2 WNV)
- Williams County: May 11 to September 28 (140 days, 31 WNV)
- Mountrail County: May 11 to September 27 (139 days, 20 WNV)
West Nile in Mercer County
From 1999 to 2025, CDC ArboNET counted 73 human West Nile cases in Mercer County (12 neuroinvasive) across 18 years. The worst was 2003 with 17; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.