Beyond MoCo: Maryland Agencies to Treat Parts of Potomac River for Black Fly Control on September 27

by MCS Staff

The Maryland Department of Agriculture (MDA) — in partnership with the Maryland Department of Natural Resources — will treat a targeted area of the Potomac River near Harpers Ferry, West Virginia, as part of a pilot program to control black fly populations in the area. Treatment is scheduled for 10 a.m. September 27, 2022.

MDA will apply a Bacillus thuringiensis israelensis (Bti)-based larvicide via helicopter (Bell 206 Long Ranger, green and white paint scheme. Tail number is N641HA). Bti is a naturally occurring bacteria found in soils worldwide. It is a bacterial insecticide, not a chemical, and is only harmful to a very limited variety of organisms, including midge, black fly, and mosquito larvae and a few other aquatic Dipteran (flies) insects. The treatment may cause temporary discoloration of the water, but it is completely nontoxic and is not harmful to humans, fish, crabs or other aquatic invertebrates. A fact sheet on Bti can be found here.​

The Black Fly Suppression Pilot Program was established in 2016. Why is Maryland treating Washington County for Black Flies? In response to black fly concerns from citizens in Washington County, Maryland, Governor Larry Hogan has allocated $200,000 for a black fly suppression pilot project (House Bill 870​), directed by Maryland Department of Agriculture (MDA) and Maryland Department of Natural Resources (DNR) in conjunction with University of Maryland Department of Entomology. The pilot black fly treatment and monitoring project will be implemented this Summer (2017) on the Potomac River in Washington County. For more information on the program, please visit MDA’s website.

Featured photo courtesy of​


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