Mosquito season in Washington County, PA: when it starts and ends
Mosquito months in Washington County
In a normal year mosquito season in Washington County, PA starts around April 12 and ends around October 25, about 28 weeks.
- Jan
- Feb
- Mar
- Apr
- May
- Jun
- Jul
- Aug
- Sep
- Oct
- Nov
- Dec
What to do in Washington County, and when
- Start tipping out standing water weekly by March 29.
- Book any yard treatment for mid April, ahead of the July peak.
- Repellent can go away after October 25.
- 3 West Nile cases since 2016 (last 2025): you should use repellent at dusk July to August, more so if over 60.
Washington County against the rest of PA
Washington County has the 14th longest season of 67 PA counties, at 196 days against 222 in Philadelphia County and 154 in Clinton County. Its mean temperature is 51.5°F.
- Montgomery County: April 12 to October 27 (198 days, 41 WNV)
- Lebanon County: April 12 to October 26 (197 days, 14 WNV)
- Cumberland County: April 13 to October 26 (196 days, 8 WNV)
- Juniata County: April 13 to October 26 (196 days, 0 WNV)
West Nile in Washington County
From 1999 to 2025, CDC ArboNET counted 4 human West Nile cases in Washington County (1 neuroinvasive) across 4 years. The worst was 2025 with 1; the latest was 2025.
More: how the dates are worked out · when the season starts across the US.