Mosquito season in San Joaquin County, CA: when it starts and ends
Mosquito months in San Joaquin County
In a normal year mosquito season in San Joaquin County, CA starts around January 27 and ends around December 7, about 45 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in San Joaquin County, and when
- Start tipping out standing water weekly by January 13.
- Book any yard treatment for late January, ahead of the July peak.
- Repellent can go away after December 7.
- 86 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to September, and check CA spray notices.
San Joaquin County against the rest of CA
San Joaquin County has the 12th longest season of 58 CA counties, at 314 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 63.3°F.
- Marin County: January 24 to December 10 (321 days, 0 WNV)
- Kern County: January 25 to December 8 (316 days, 173 WNV)
- Solano County: January 28 to December 7 (313 days, 18 WNV)
- San Bernardino County: January 30 to December 8 (312 days, 122 WNV)
West Nile in San Joaquin County
From 1999 to 2025, CDC ArboNET counted 206 human West Nile cases in San Joaquin County (114 neuroinvasive) across 22 years. The worst was 2005 with 34; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.