Mosquito season in Pima County, AZ: when it starts and ends
Mosquito months in Pima County
In a normal year mosquito season in Pima County, AZ starts around March 6 and ends around November 21, about 37 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Pima County, and when
- Start tipping out standing water weekly by February 20.
- Book any yard treatment for early March, ahead of the July peak.
- Repellent can go away after November 21.
- 142 West Nile cases since 2016: you should wear EPA-registered repellent at dusk May to September, and check AZ spray notices.
Pima County against the rest of AZ
Pima County has the 7th longest season of 15 AZ counties, at 260 days against 364 in Maricopa County and 150 in Coconino County. Its mean temperature is 66.8°F.
- Gila County: February 2 to December 7 (308 days, 9 WNV)
- Santa Cruz County: February 23 to November 30 (280 days, 2 WNV)
- Graham County: March 13 to November 16 (248 days, 6 WNV)
- Cochise County: March 27 to November 13 (231 days, 4 WNV)
West Nile in Pima County
From 1999 to 2025, CDC ArboNET counted 342 human West Nile cases in Pima County (234 neuroinvasive) across 21 years. The worst was 2021 with 103; the latest was 2025.
More: how the dates are worked out · reading the West Nile counts.