Mosquito season in Sonoma County, CA: when it starts and ends
Mosquito months in Sonoma County
In a normal year mosquito season in Sonoma County, CA starts around February 4 and ends around December 4, about 43 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Sonoma County, and when
- Start tipping out standing water weekly by January 21.
- Book any yard treatment for early February, ahead of the August peak.
- Repellent can go away after December 4.
- 1 West Nile case since 2016 (last 2023): you should use repellent at dusk August, more so if over 60.
Sonoma County against the rest of CA
Sonoma County has the 21st longest season of 58 CA counties, at 302 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 57.8°F.
- Sutter County: February 2 to December 3 (304 days, 29 WNV)
- Butte County: February 4 to December 3 (303 days, 95 WNV)
- Yolo County: February 6 to December 2 (300 days, 93 WNV)
- Colusa County: February 5 to December 1 (299 days, 7 WNV)
West Nile in Sonoma County
From 1999 to 2025, CDC ArboNET counted 3 human West Nile cases in Sonoma County (3 neuroinvasive) across 3 years. The worst was 2023 with 1; the latest was 2023.
More: how the dates are worked out · when the season starts across the US.