Mosquito season in Petroleum County, MT: when it starts and ends
Mosquito months in Petroleum County
In a normal year mosquito season in Petroleum County, MT starts around May 7 and ends around September 29, about 21 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Petroleum 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 29.
- No West Nile cases since 2016, so bites in Petroleum County are a nuisance; check window screens.
Petroleum County against the rest of MT
Petroleum County has the 20th longest season of 56 MT counties, at 145 days against 163 in Dawson County and 89 in Gallatin County. Its mean temperature is 46°F.
- Broadwater County: May 7 to October 1 (147 days, 1 WNV)
- Musselshell County: May 7 to October 1 (147 days, 0 WNV)
- Pondera County: May 10 to October 2 (145 days, 1 WNV)
- Garfield County: May 8 to September 29 (144 days, 1 WNV)
West Nile in Petroleum County
From 1999 to 2025, CDC ArboNET counted 1 human West Nile case in Petroleum County (0 neuroinvasive) across 1 year. The worst was 2007 with 1; the latest was 2007.
Background: when mosquitoes go away for the winter; how the dates are worked out.