Mosquito season in Stanislaus County, CA: when it starts and ends

Mosquito months in Stanislaus County

In a normal year mosquito season in Stanislaus County, CA starts around January 30 and ends around December 5, about 44 weeks.

1. Jan
2. Feb
3. Mar
4. Apr
5. May
6. Jun
7. Jul
8. Aug
9. Sep
10. Oct
11. Nov
12. Dec

What to do in Stanislaus County, and when

• Start tipping out standing water weekly by January 16.
• Book any yard treatment for late January, ahead of the July peak.
• Repellent can go away after December 5.
• 180 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to September, and check CA spray notices.

Stanislaus County against the rest of CA

Stanislaus County has the 16th longest season of 58 CA counties, at 310 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 63.4°F.

• San Bernardino County: January 30 to December 8 (312 days, 122 WNV)
• Sacramento County: January 29 to December 5 (310 days, 131 WNV)
• Alameda County: February 3 to December 6 (305 days, 4 WNV)
• Contra Costa County: February 8 to December 10 (305 days, 35 WNV)

West Nile in Stanislaus County

From 1999 to 2025, CDC ArboNET counted 438 human West Nile cases in Stanislaus County (238 neuroinvasive) across 21 years. The worst was 2005 with 84; the latest was 2025.

See how the dates are worked out, and reading the West Nile counts.