Eurasian Water Milfoil

In 2009, Eurasian water milfoil (EWM) was found and confirmed in Becker Lake. The residents of Long Lake in Manitowoc County have been battling this plant for years. Now it's in Becker Lake, too. It has been a problem on Lake Winnebago for many years.

EWM is the only non-native milfoil in Wisconsin. It has slender stems whorled by feathery leaves and tiny flowers produced above the water surface. The leaves are threadlike, typically uniform in diameter. Eurasian water milfoil has 9-21 pairs of leaflets per leaf, while the native Northern milfoil typically has 7-11 pairs of leaflets.

EWM reproduces vegetatively by fragmentation. The plant produces fragments after fruiting once or twice during the summer. These shoots may be inadvertently picked up by boaters. EWM is readily moved between waterbodies by boats, motors, trailers, bilges, live wells, or bait buckets, and can live for weeks if kept moist.

Once established, EWM reproduces from shoot fragments and runners that creep along the lake bed. It spreads rapidly by fragmentation and blocks out sunlight needed for native plant growth often resulting in monotypic stands, threatening the integrity of aquatic communities.

Dense stands of EWM also restrict recreational uses like swimming, boating, and fishing. EWM may also lead to deteriorating water quality and algae blooms in infested lakes.

Lake managers and lakeshore property owners should check for new colonies and control them before they spread. The plants can be hand pulled or raked. It is imperative that all fragments be removed from the water and the shore.

Department of Natural Resources permits are required for chemical treatments, mechanical treatments, and some manual treatments. For further information on chemical controls, visit the DNR website at www.dnr.state.wi.us/invasives/fact/milfoil.htm

Hand pulling is the preferred control method for small colonies. The process is thorough and selective (not to mention time-consuming) yet special care must be taken to collect all roots and plant fragments.

Chemical Control: Herbicide treatment is not recommended because it is typically disruptive to aquatic ecosystems and not selective in the vegetation it affects, thus threatening native plants.

EWM spreads vegetatively by plant fragments, so it is important to clean all vegetation off boats and equipment before leaving water access. Remember to inspect all your equipment, remove attached plants or animals and drain all the water from your equipment.