Mosquito season in Mesa County, CO: when it starts and ends

Mosquito months in Mesa County

In a normal year mosquito season in Mesa County, CO starts around April 8 and ends around October 25, about 29 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 Mesa County, and when

• Start tipping out standing water weekly by March 25.
• Book any yard treatment for early April, ahead of the July peak.
• Repellent can go away after October 25.
• 29 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check CO spray notices.

Mesa County against the rest of CO

Mesa County has the 1st longest season of 64 CO counties, at 200 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 54°F.

• Bent County: April 18 to October 21 (186 days, 3 WNV)
• Prowers County: April 18 to October 20 (185 days, 9 WNV)

West Nile in Mesa County

From 1999 to 2025, CDC ArboNET counted 306 human West Nile cases in Mesa County (88 neuroinvasive) across 17 years. The worst was 2004 with 127; the latest was 2025.

See how the dates are worked out, and reading the West Nile counts.