Mosquito season in San Luis Obispo County, CA: when it starts and ends

Mosquito months in San Luis Obispo County

In a normal year mosquito season in San Luis Obispo County, CA starts around February 22 and ends around November 21, about 39 weeks.

What to do in San Luis Obispo County, and when

Start tipping out standing water weekly by February 8.
Book any yard treatment for late February, ahead of the August peak.
Repellent can go away after November 21.
6 West Nile cases since 2016 (last 2023): you should use repellent at dusk July to August, more so if over 60.

San Luis Obispo County against the rest of CA

San Luis Obispo County has the 33rd longest season of 58 CA counties, at 272 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 60.1°F.

Yuba County: February 27 to November 28 (274 days, 24 WNV)
Santa Barbara County: February 27 to November 27 (273 days, 2 WNV)
Calaveras County: March 4 to November 26 (267 days, 2 WNV)
Glenn County: March 1 to November 22 (266 days, 18 WNV)

West Nile in San Luis Obispo County

From 1999 to 2025, CDC ArboNET counted 8 human West Nile cases in San Luis Obispo County (5 neuroinvasive) across 5 years. The worst was 2023 with 2; the latest was 2023.

More: how the dates are worked out · reading the West Nile counts.