Eurasian Watermilfoil in Vermont

         Eurasian watermilfoil (Myriophyllum spicatum) is an aquatic invasive species that is quickly becoming a serious problem in Vermont lakes. Originating from Europe, Asia, and northern Africa, milfoil is most commonly found in shallow bays and along the shoreline of lakes.

Washington Department of Ecology,  2011

            Milfoil is a perennial, and is known for both growing and spreading quickly. It has the ability to spread so rapidly because any fragment that breaks from the parent plant has the capability of starting a whole new growth. This fragmentation occurs naturally from wind and waves, and through recreational activities like swimming and boating. In Vermont, Eurasian watermilfoil is spreading through lakes primarily due to human recreational activities. Pieces cling to boats, trailers, and other equipment and are transferred to other aquatic ecosystems. Actually, it is illegal to transport Eurasian watermilfoil to or from any Vermont surface water.

            Milfoil has a profound impact on an ecosystem largely because of the way it forms into dense mats of vegetation on the surface of the water. These mats block the light necessary for other native species to survive, and reduce the available spawning grounds for fish. Additionally, the presence of milfoil causes secondary effects like increased sedimentation, a decrease in oxygen levels, and increased mosquito activity in an area. 

                                                                                  CWMA, 2010

            Once milfoil has found it’s way into a lake, there is no known, safe way to eradicate it. Some success has been found using aquatic and non-aquatic herbicides, but little is known about their long-term effects on an ecosystem. Other control methods include harvesting, underwater roto-tilling, diver hand pulling, or diver dredging. These controls are not completely effective because of the milfoils characteristic ability to reproduce by fragmentation. New investigative research is being conducted on biological controls, like milfoil weevils and introduction of certain types of carp. 

                                                                                      Franz, 2011

Article: Weevils as a Biological Control

           Recent studies have shown that a native, herbivorous weevil may have a significant role in causing the decline of Eurasian watermilfoil in Vermont. Because Eurasian watermilfoil is such a hazard to aquatic ecosystems, and there are no proven eradication methods, the possibility of weevils as a natural biological control is particularly interesting. Past studies have shown that watermilfoil has declined in 24 of the 37 Vermont lakes where weevils are naturally occurring. This non-random pattern of decline supports the theory that the weevils are acting as a biological control. Unfortunately, despite this promising correlation, there is no concrete evidence to support the effectiveness of weevils on milfoil.

            Research is still being conducted, in hopes that the North American Weevil will become a reliable future control for Vermont lakes infested with Eurasian watermilfoil. Work is also being done to make sure that during these trial periods weevils from other states are not being introduced into the Vermont ecosystems, possibly bringing parasites and diseases that would harm native populations. 

By Meagan Murray

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   Holm, L. G. (1970) Aquatic Weeds. Tropical Pest Management 16(4)
   Shearer, Judy F. (1994) Potential Role of Plant Pathogens in Declines of Submersed Macrophytes. Lake and Reservoir Management 10(1)