Thursday, July 31, 2014
Eurasian Watermilfoil Control

Once Eurasian watermilfoil is established, there is no known way to completely eradicate it. The best strategy is to control existing stands and limit its spread to other parts of the lake. Since Eurasian watermilfoil spreads by fragmentation, harvesting is not recommended because this may spread it to other parts of the lake. In addition, like lawn mowing, harvesting only reduces the height of the plant temporarily and requires repeated cutting, which can be expensive.

Currently, Eurasian watermilfoil can be controlled using mechanical/physical and or biological controls.

Eurasian watermilfoil. Robert Johnson, Cornell University. Ruthanna Hawkins, Cayuga Lake Watershed Network. Used with permission.
Eurasian watermilfoil. Robert Johnson, Cornell University. Ruthanna Hawkins, Cayuga Lake Watershed Network. Used with permission.

Mechanical/Physical Control Methods for Eurasian Watermilfoil

Bottom barriers/Benthic Mats

Light-blocking bottom barriers, or benthic mats, block sunlight from reaching plants underneath and prevent growth and seed production. However, they are not species specific and may degrade fish spawning habitat.

Installation of a benthic barrier
Installation of a benthic barrier

Barriers are most appropriate for localized areas such as swimming areas, around docks, and in boat lanes. Landscaping fabric or geotextile fabric is anchored to the bottom with slits cut in it to allow air bubbles to escape.

Bottom barriers require a permit from the NYS Department of Environmental Conservation.Please check with the New York State Department of Environmental Conservation before any work is done to get any permits that may be required. Contact them by phone: 

  • At (315) 426-7400 for Region 7 which includes Broome, Cayuga, Chenango, Cortland, Onondaga, Oswego, Madison, Tioga and Tompkins counties.

  • At (585) 226-2466 for Region 8 which includes Orleans, Monroe, Wayne, Genesee, Livingston, Ontario, Yates, Seneca, Steuben, Schuyler and Chemung counties.

More information on the permit process can be found in the document below from the New York State Department of Environmental Conservation:


The following documents were developed by Onondaga County Cooperative Extension: Please note, in order to view PDF documents, you must have Adobe Acrobat Reader installed on your computer. If you do not have this software, click here to download a free copy now

Suction dredging

Requires a qualified diver and special hoses that suck up all parts of the plant from the sediment. This procedure is plant specific and can reduce mass. However, it may cost up to $165-$250, 500 sq. ft/hour and can stir up sediment.

Suction dredging requires a permit from the NYS Department of Environmental Conservation.Please check with the New York State Department of Environmental Conservation before any work is done to get any permits that may be required. Contact them by phone:

  • At (315) 426-7400 for Region 7 which includes Broome, Cayuga, Chenango, Cortland, Onondaga, Oswego, Madison, Tioga and Tompkins counties.

  • At (585) 226-2466 for Region 8 which includes Orleans, Monroe, Wayne, Genesee, Livingston, Ontario, Yates, Seneca, Steuben, Schuyler and Chemung counties.

More information on the permit process can be found in the document below from the New York State Department of Environmental Conservation:


Please note, in order to view PDF documents, you must have Adobe Acrobat Reader installed on your computer. If you do not have this software, click here to download a free copy now

Biological Control of Eurasian Watermilfoil

In some circumstances predators or herbivores may help reduce populations of aquatic weeds. Any time non-native biological herbivores are introduced to an area in efforts to control an invasive plant, much research must be done in advance to ensure that the herbivore prefers the plant in the experimental stage "exclusively" to avoid herbivory of beneficial, native plants and future invasive species issues. Researchers from Cornell University are experimenting with an aquatic moth (Acentria ephemerella) and aquatic weevil (Euhrychiopsis lecontei):

An aquatic moth (Acentria ephemerella) from Europe uses watermilfoil as a food source, and thereby limits the spread of the plant. Around 1927, the moth was introduced to North America and often feeds on Eurasian watermilfoil.

An aquatic weevil native to North America (Euchrychiopsis lecontei) is a "food specialist" and historically fed primarily on the native Northern Watermilfoil. The weevil also carrys out its life cycle on Eurasian watermilfoil and seems to provide short-term reductions in plant growth in areas where the weevil populations are high enough.