Mosquito season in Shasta County, CA: when it starts and ends
Mosquito months in Shasta County
In a normal year mosquito season in Shasta County, CA starts around February 20 and ends around November 28, about 40 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Shasta County, and when
- Start tipping out standing water weekly by February 6.
- Book any yard treatment for mid February, ahead of the July peak.
- Repellent can go away after November 28.
- 16 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to September, and check CA spray notices.
Shasta County against the rest of CA
Shasta County has the 28th longest season of 58 CA counties, at 280 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 62.4°F.
- Merced County: February 12 to November 27 (288 days, 60 WNV)
- Ventura County: February 17 to December 1 (287 days, 13 WNV)
- Tulare County: February 23 to November 28 (278 days, 125 WNV)
- Napa County: February 24 to November 27 (276 days, 1 WNV)
West Nile in Shasta County
From 1999 to 2025, CDC ArboNET counted 43 human West Nile cases in Shasta County (28 neuroinvasive) across 17 years. The worst was 2007 with 9; the latest was 2024.
Background: reading the West Nile counts; how the dates are worked out.