Mosquito Control - Larviciding, etc

Proactive Storm Drain Larviciding

Picture of the bottom of a catch basin full of trash
Storm drains, also called storm sewers or storm water catch basins, are located throughout the county. Storm drains usually drain well and do not present a problem as far as mosquito breeding; however, some may have structural problems or may be partially blocked, retain water and produce excellent breeding sites for the mosquito vectors of West Nile virus. This is particularly common in older communities in the County.

The Health Department treats storm drains throughout the County with a larvicide, an insecticide used to kill mosquito larvae, in programmed cycles aimed at reducing mosquito populations that breed in this environment. The first treatment cycle typically begins in May each year, with the number and magnitude of each cycle dependent on climatic factors and mosquito surveillance results.

The Department of Public Works and Environmental Services will ensure larviciding of storm water retention ponds countywide where deemed necessary.

The Fairfax County West Nile Virus Surveillance Program will work closely with the Park Authority to manage vector mosquito populations in parks when necessary. Nuisance mosquito breeding sites will not be routinely treated.


In the history of West Nile virus in Fairfax County, the use of spray insecticides against adult mosquitoes has not been necessary. However, if mosquito surveillance data indicates that the level of West Nile virus activity poses a significant threat to human health; adult mosquitoes will be controlled with adulticides.

Contact Fairfax County: Phone, Email or Twitter | Main Address: 12000 Government Center Parkway, Fairfax, VA 22035
Technical Questions: Web Administrator

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