Mosquito season in Garfield County, MT: when it starts and ends
Mosquito months in Garfield County
In a normal year mosquito season in Garfield County, MT starts around May 8 and ends around September 29, about 21 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Garfield County, and when
- Start tipping out standing water weekly by April 24.
- Book any yard treatment for early May, ahead of the July peak.
- Repellent can go away after September 29.
- 1 West Nile case since 2016 (last 2018): you should use repellent at dusk July to July, more so if over 60.
Garfield County against the rest of MT
Garfield County has the 22nd longest season of 56 MT counties, at 144 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 43.9°F.
- Petroleum County: May 7 to September 29 (145 days, 0 WNV)
- Pondera County: May 10 to October 2 (145 days, 1 WNV)
- Flathead County: May 8 to September 28 (143 days, 1 WNV)
- Chouteau County: May 9 to September 29 (143 days, 1 WNV)
West Nile in Garfield County
From 1999 to 2025, CDC ArboNET counted 7 human West Nile cases in Garfield County (1 neuroinvasive) across 4 years. The worst was 2003 with 4; the latest was 2018.
More: how the dates are worked out · when the season starts across the US.