Mosquito season in Fresno County, CA: when it starts and ends
Mosquito months in Fresno County
In a normal year mosquito season in Fresno County, CA starts around January 22 and ends around December 10, about 46 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Fresno County, and when
- Start tipping out standing water weekly by January 8.
- Book any yard treatment for late January, ahead of the July peak.
- Repellent can go away after December 10.
- 201 West Nile cases since 2016: you should wear EPA-registered repellent at dusk May to September, and check CA spray notices.
Fresno County against the rest of CA
Fresno County has the 9th longest season of 58 CA counties, at 321 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 66°F.
- San Mateo County: December 31 to December 12 (347 days, 5 WNV)
- Santa Clara County: January 18 to December 11 (327 days, 16 WNV)
- Marin County: January 24 to December 10 (321 days, 0 WNV)
- Kern County: January 25 to December 8 (316 days, 173 WNV)
West Nile in Fresno County
From 1999 to 2025, CDC ArboNET counted 430 human West Nile cases in Fresno County (215 neuroinvasive) across 22 years. The worst was 2005 with 59; the latest was 2025.
Background: reading the West Nile counts; how the dates are worked out.