Milfoil Management

EWM Management a Top Priority

In 2008, the Commission received a WDNR grant to begin management of EWM on the Eagle River Chain using herbicide treatments. The Commission has received multiple grants since then, and the management program continues.

Treatment on the Eagle River Chain has been extremely successful in terms of controlling the density and occurrence of EWM. Over the course of annual treatments from 2008 to 2018, EWM acreage has been reduced from 278 acres in 2007 to acres 30 acres in 2018.

It took 8 years of herbicide management to bring the milfoil down to the current level. The goal of management strategy has shifted from substantial population reduction to containing and maintaining the population at a low, suppressed level of occurrence.

Not wanting to abandon management and simply wait for EWM populations to reach levels that are again applicable for herbicide control, the Commission used a professional-based hand-harvesting program to keep the milfoil at a manageable level in 2016, 2017 and 2018.

Hand removal of invasive plants is the most intuitive of control methods. It is labor intensive as it involves removing and bagging the entire plant by hand. During hand harvesting, divers manually remove milfoil plants from the lake bottom, with care taken to remove the entire root crown and not to create fragments. This method is suitable for very early infestations of milfoil and for follow-up removal after herbicide treatments

During hand pulling, divers dig around and beneath the plant roots with their hands or with a tool and gently lift the entire plant out of the sediment. The ease of removal is dependent on sediment type. Divers can readily remove milfoil plants from loose or flocculent sediments. In hard sediments or rocky substrate, divers must use hand tools to loosen the root crown before they can dislodge the plant. Sometimes divers leave fine roots behind; these will not regrow, but it is important to remove the root crown (the fleshy, fibrous roots at the base of the stem).

In addition to hand harvesting, Diver Assisted Suction Harvest (DASH) was employed for the first time in 2017and used exclusively in 2018. DASH utilizes divers to hand remove aquatic invasive plants from the lake-bed. Instead of divers coming to the surface to dispose of the removed plants, plants are fed into a suction line that transports plants to the surface. DASH is NOT bottom dredging.

The entire chain is surveyed several times each year in search of EWM. One of the surveys done each summer is by trained Eagle River Chain of Lakes Association (ERCLA) volunteers utilizing GPS technology. The other surveys are completed by professional lake ecologists.