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

Mosquito months in Imperial County

In a normal year mosquito season in Imperial County, CA starts around January 2 and ends around December 29, about 52 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 Imperial County, and when

• Start tipping out standing water weekly by December 19.
• Book any yard treatment for early January, ahead of the August peak.
• Repellent can go away after December 29.
• 7 West Nile cases since 2016 (last 2020): you should use repellent at dusk April to October, more so if over 60.

Imperial County against the rest of CA

Imperial County has the 4th longest season of 58 CA counties, at 361 days against 365 in Los Angeles County and 110 in Mono County. Its mean temperature is 73.6°F.

• Orange County: all year (365 days, 117 WNV)
• San Francisco County: all year (365 days, 2 WNV)
• Santa Cruz County: January 3 to December 27 (358 days, 1 WNV)
• Riverside County: January 10 to December 31 (355 days, 110 WNV)

West Nile in Imperial County

From 1999 to 2025, CDC ArboNET counted 17 human West Nile cases in Imperial County (10 neuroinvasive) across 11 years. The worst was 2019 with 3; the latest was 2020.

More: how the dates are worked out · where mosquitoes never stop.