Mosquito season in Knox County, MO: when it starts and ends

Mosquito months in Knox County

In a normal year mosquito season in Knox County, MO starts around April 9 and ends around October 25, about 28 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 Knox County, and when

• Start tipping out standing water weekly by March 26.
• Book any yard treatment for early April, ahead of the July peak.
• Repellent can go away after October 25.
• No West Nile cases since 2016, so bites in Knox County are a nuisance; check window screens.

Knox County against the rest of MO

Knox County has the 95th longest season of 115 MO counties, at 199 days against 242 in Pemiscot County and 187 in Crawford County. Its mean temperature is 51.8°F.

• Monroe County: April 11 to October 28 (200 days, 0 WNV)
• Dallas County: April 9 to October 25 (199 days, 1 WNV)
• Clinton County: April 10 to October 26 (199 days, 1 WNV)
• Madison County: April 10 to October 26 (199 days, 0 WNV)

West Nile in Knox County

CDC ArboNET lists no human West Nile cases for Knox County from 1999 to 2025, though virus turned up in birds, mosquitoes or horses in 2 of those years.

Background: when mosquitoes go away for the winter; how the dates are worked out.