Mosquito season in Yolo County, CA: when it starts and ends
Mosquito months in Yolo County
In a normal year mosquito season in Yolo County, CA starts around February 6 and ends around December 2, about 43 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Yolo County, and when
- Start tipping out standing water weekly by January 23.
- Book any yard treatment for early February, ahead of the July peak.
- Repellent can go away after December 2.
- 93 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to September, and check CA spray notices.
Yolo County against the rest of CA
Yolo County has the 22nd longest season of 58 CA counties, at 300 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 62.2°F.
- Butte County: February 4 to December 3 (303 days, 95 WNV)
- Sonoma County: February 4 to December 4 (302 days, 1 WNV)
- Colusa County: February 5 to December 1 (299 days, 7 WNV)
- Kings County: February 5 to November 30 (298 days, 57 WNV)
West Nile in Yolo County
From 1999 to 2025, CDC ArboNET counted 176 human West Nile cases in Yolo County (77 neuroinvasive) across 20 years. The worst was 2023 with 39; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.