Mosquito season in Nelson County, ND: when it starts and ends

Mosquito months in Nelson County

In a normal year mosquito season in Nelson County, ND starts around May 7 and ends around September 30, about 21 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 Nelson County, and when

• Start tipping out standing water weekly by April 23.
• Book any yard treatment for early May, ahead of the July peak.
• Repellent can go away after September 30.
• 1 West Nile case since 2016 (last 2018): you should use repellent at dusk July, more so if over 60.

Nelson County against the rest of ND

Nelson County has the 36th longest season of 53 ND counties, at 145 days against 160 in Sheridan County and 135 in Rolette County. Its mean temperature is 39°F.

• Ramsey County: May 7 to September 30 (146 days, 12 WNV)
• Steele County: May 7 to September 30 (146 days, 2 WNV)
• Pierce County: May 7 to September 29 (145 days, 4 WNV)
• Benson County: May 8 to September 30 (145 days, 4 WNV)

West Nile in Nelson County

From 1999 to 2025, CDC ArboNET counted 9 human West Nile cases in Nelson County (5 neuroinvasive) across 6 years. The worst was 2012 with 2; the latest was 2018.

Background: when the season starts across the US; how the dates are worked out.