Mosquito season in San Juan County, NM: when it starts and ends

Mosquito months in San Juan County

In a normal year mosquito season in San Juan County, NM starts around April 17 and ends around October 25, about 27 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 San Juan County, and when

• Start tipping out standing water weekly by April 3.
• Book any yard treatment for mid April, ahead of the July peak.
• Repellent can go away after October 25.
• 49 West Nile cases since 2016: you should wear EPA-registered repellent at dusk June to August, and check NM spray notices.

San Juan County against the rest of NM

San Juan County has the 18th longest season of 33 NM counties, at 191 days against 268 in Doña Ana County and 114 in Catron County. Its mean temperature is 53.3°F.

• Valencia County: April 8 to October 31 (206 days, 20 WNV)
• Otero County: April 20 to October 30 (193 days, 3 WNV)
• Lincoln County: April 24 to October 24 (183 days, 3 WNV)
• Los Alamos County: April 21 to October 17 (179 days, 1 WNV)

West Nile in San Juan County

From 1999 to 2025, CDC ArboNET counted 142 human West Nile cases in San Juan County (85 neuroinvasive) across 21 years. The worst was 2004 with 34; the latest was 2025.

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