Mosquito season in Rosebud County, MT: when it starts and ends
Mosquito months in Rosebud County
In a normal year mosquito season in Rosebud County, MT starts around May 3 and ends around October 6, about 22 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Rosebud 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 6.
- 3 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Rosebud County against the rest of MT
Rosebud County has the 7th longest season of 56 MT counties, at 156 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 46.1°F.
- Yellowstone County: April 30 to October 4 (157 days, 26 WNV)
- Richland County: May 2 to October 6 (157 days, 13 WNV)
- Prairie County: May 2 to October 5 (155 days, 1 WNV)
- Sweet Grass County: May 3 to October 5 (155 days, 1 WNV)
West Nile in Rosebud County
From 1999 to 2025, CDC ArboNET counted 24 human West Nile cases in Rosebud County (9 neuroinvasive) across 7 years. The worst was 2003 with 11; the latest was 2025.
See how the dates are worked out, and when the season starts across the US.