Mosquito season in Delta County, CO: when it starts and ends
Mosquito months in Delta County
In a normal year mosquito season in Delta County, CO starts around April 25 and ends around October 16, about 25 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Delta County, and when
- Start tipping out standing water weekly by April 11.
- Book any yard treatment for late April, ahead of the July peak.
- Repellent can go away after October 16.
- 111 West Nile cases since 2016: you should wear EPA-registered repellent at dusk July to August, and check CO spray notices.
Delta County against the rest of CO
Delta County has the 14th longest season of 64 CO counties, at 174 days against 200 in Mesa County and 69 in Summit County. Its mean temperature is 49.5°F.
- Kit Carson County: April 27 to October 19 (175 days, 7 WNV)
- El Paso County: April 24 to October 15 (174 days, 66 WNV)
- Washington County: April 27 to October 16 (172 days, 6 WNV)
- Morgan County: April 27 to October 15 (171 days, 23 WNV)
West Nile in Delta County
From 1999 to 2025, CDC ArboNET counted 231 human West Nile cases in Delta County (62 neuroinvasive) across 20 years. The worst was 2006 with 34; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.