Mosquito season in Colusa County, CA: when it starts and ends
Mosquito months in Colusa County
In a normal year mosquito season in Colusa County, CA starts around February 5 and ends around December 1, about 43 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Colusa County, and when
- Start tipping out standing water weekly by January 22.
- Book any yard treatment for early February, ahead of the July peak.
- Repellent can go away after December 1.
- 7 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to September, more so if over 60.
Colusa County against the rest of CA
Colusa County has the 23rd longest season of 58 CA counties, at 299 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 62.1°F.
- Sonoma County: February 4 to December 4 (302 days, 1 WNV)
- Yolo County: February 6 to December 2 (300 days, 93 WNV)
- Kings County: February 5 to November 30 (298 days, 57 WNV)
- Tehama County: February 7 to November 30 (297 days, 15 WNV)
West Nile in Colusa County
From 1999 to 2025, CDC ArboNET counted 25 human West Nile cases in Colusa County (8 neuroinvasive) across 14 years. The worst was 2006 with 4; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.