Mosquito season in Washington County, MD: when it starts and ends
Mosquito months in Washington County
In a normal year mosquito season in Washington County, MD starts around April 6 and ends around October 31, about 30 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 23.
- Book any yard treatment for early April, ahead of the July peak.
- Repellent can go away after October 31.
- 3 West Nile cases since 2016 (last 2025): you should use repellent at dusk June to August, more so if over 60.
Washington County against the rest of MD
Washington County has the 21st longest season of 24 MD counties, at 208 days against 235 in Wicomico County and 175 in Garrett County. Its mean temperature is 54.3°F.
- Cecil County: April 4 to November 4 (215 days, 5 WNV)
- Harford County: April 5 to November 2 (211 days, 9 WNV)
- Allegany County: April 6 to October 28 (205 days, 0 WNV)
- Carroll County: April 9 to October 29 (203 days, 4 WNV)
West Nile in Washington County
From 1999 to 2025, CDC ArboNET counted 12 human West Nile cases in Washington County (8 neuroinvasive) across 8 years. The worst was 2003 with 4; the latest was 2025.
More: how the dates are worked out · when the season starts across the US.