Eurasian Watermilfoil 
(Myriophyllum spicatum)

What is Eurasian Watermilfoil?

Eurasian Watermilfoil is an invasive species of an aquatic plant native to Europe, Asia and North Africa. Its first documented sighting in North America was in 1942 in the District of Columbia. It was most likely brought to this continent in the ballast of a ship and has since spread to almost every continental state and throughout Canada.

What does Eurasian Watermilfoil look like?

Why is it a problem?

Eurasian Watermilfoil spreads easily and grows quickly. Eurasian Watermilfoil crowds out native plants reducing biodiversity, diminishes fish habitat and negatively impacts wetland habitats. Dense growths inhibit water recreation like boating, swimming and fishing. Eurasian Watermilfoil also adversely affects the local tourist-dependent economy by decreasing recreational utility.

How does Eurasian Watermilfoil spread?
The primary way Eurasian Watermilfoil spreads is through vegetative reproduction. This spread is mainly through fragmentation of plant tips or through root expansion.  With fragmentation, even a very small piece of the aquatic plant can float away, re-root and begin a new colony. This milfoil can form thick, floating mats of vegetation, clogging the water and hindering recreation. Eurasian Watermilfoil can grow in water 0 .5-10 meters deep.

How much of a threat does Eurasian Watermilfoil represent to Lake George?
The map at the right (click on it to enlarge) was created using GIS mapping software. It is an attempt to illustrate the threat that milfoil poses to Lake George. The two bands shaded in light and dark red are bathymetric readings showing depths of 0-5 meters and 5-10 meters, which is approximately the range in which milfoil may grow. The green dots represent documented milfoil sites (over 144 total), and the yellow triangles represent the locations of dense beds of milfoil.

What can be done?
Several aquatic plant management techniques exist to control the spread of milfoil, and all have strengths and weaknesses. Methods available include biological, chemical and physical controls. Individual incidences of Eurasian Watermilfoil must be evaluated prior to determining the method that would be most effective and economic, environmental and technical constraints must also be considered. Below are some of the most common forms of biological, chemical, mechanical and physical controls.

Biological Controls: Controlling exotic species through the use of biocontrols has become a popular area of study in recent years.

 Watermilfoil Weevil (Euhrychiopsis lecontei): This native herbivorous weevil has been considered as a possible biocontrol for the spread of Eurasian Watermilfoil. Adult weevils have been shown to prefer Eurasian Watermilfoil over the native species and they feed on the meristem, leaves and stems of the Eurasian Watermilfoil, causing loss of buoyancy, stem weakening, removal of leaves and disruption of the passage of nutrients throughout the plant. An advantage of the weevil is that it is a native species and self-reproducing. A drawback of the use of weevils is that often biocontrols and mechanical harvesting are used in combination to control the spread of EWM.   Mechanical harvesting removes the top 1-6 feet of the milfoil plants, the preferred feeding area for the weevils. The effectiveness of the weevil to inhibit Eurasian Watermilfoil over a sustained period of time is still being studied.

Chemical Controls:

• Fluridone: The herbicide fluridone (SONAR) is designed to treat larger areas (greater than .5 acres) of medium to high density Eurasian Watermilfoil. A Generic Environmental Impact Statement was prepared in 1995 regarding the use of fluridone finding strong potential for fluridone to be effective in preventing the spread of Eurasian Watermilfoil in the waters of New York State. The Generic Environmental Impact Statement also indicated minimal adverse impacts to non-target organisms. (Fluridone is the active ingredient in SONAR. Fluridone is absorbed by plant tissues and transported throughout the plant. Fluridone obtained Federal registration in 1986 and has been in widespread use outside New York since the late 1980s. Full use in New York State was approved in 1995.)

Mechanical Controls:

• Mechanical Harvesting: Mechanical harvesting is not a permanent control for the spread of Eurasian Watermilfoil. The milfoil grows back and fragmentation is very likely to occur during harvesting, spreading the milfoil to other areas and creating an even larger problem.

• Rotovation: Rotovation is simply a large underwater rototiller.  The Rotovator operator maneuvers the machinery in a crosshatch pattern to unearth the root crowns of the Eurasian Watermilfoil. The material tilled needs to then be collected.  The negative side to Rotovation is that cutting the plants and failing to remove all the fragments can lead to the accelerated spread of the plant.

• Suctioning: A diver-operated vacuum lift is used to remove plant stems, roots and leaves. Sediment is not removed.  This process is slow and cost intensive.  It is useful in smaller areas of nuisance species populations.

Physical Controls:

• Bottom Barriers “Matting”: Barriers are materials that are placed on sections of lakes of river bottoms and are attached to the bottom with pins of sand bags. The barriers are used to reduce light levels and inhibit growth of Eurasian Watermilfoil, but also have shown to inhibit the growth of native species for 1-2 years following barrier removal, with EWM returning to full strength.

• Hand Pulling: Hand pulling is similar to weeding in a garden and can be effective in relatively small areas with small occurrences of Eurasian Watermilfoil.  Special care must be taken to ensure that the entire plant (leaves, stems and roots) is removed.

• Water Level Drawdown: A water level control structure is used to lover the level of the water body or “De-Water” the water body for an extended period of time. Drawdown is only useful for water bodies with water level controls in place. Effective drawdown should remove the water to a given depth and must be at least one month in length to allow for thorough drying. Although often effective, drawdown can have damaging environmental and biological impacts to non-target species, can temporarily ruin the aesthetics of an area, impede water recreation and also may interfere with drinking water supply.

Eurasian Watermilfoil & Lake George:
Eurasian Watermilfoil was first discovered in Lake George in 1985. By 2007, the aquatic plant had spread to 157 known sites, over 2 dozen of which contain dense growths. Several methods to control milfoil in Lake George have been used including hand pulling and matting; however, no large-scale control for moderate to high-density areas has been used to date.

Lake Organizations Prompt Study of Milfoil:
Concern by the spread of milfoil in Lake George, several organizations, including the Lake George Association, New York Department of Environmental Conservation, Lake George Park Commission and the Fund for Lake George prompted a review of Eurasian Watermilfoil in Lake George in 1995. Fugro East, an environmental consulting firm developed a comprehensive management plan for the control of Eurasian Watermilfoil in Lake George. The goal of the plan is to eliminate Eurasian Watermilfoil in Lake George through the use of hand and suction harvesting, matting and with fluridone.

For more information please contact the LGA at (518) 668-3558.