AIS / Fisheries

August AIS: Eurasian Water Milfoil

Submersed aquatic plant with 3-4 feather like leaves arranged in a circle around the stem. Each feather-like leave has 12 or more pairs of leaflets whereas native Northern water milfoil has less than 10 pairs. Monitoring and prevention are key to controlling the spread!

Eurasian Water MilfoilDescription

  • Submersed aquatic plant
  • 3-4 feather-like leaves in circle around stem
  • Leaves are divided into 12 or more pairs of threadlike leaflets (native northern water milfoil has 10 or fewer pairs)
  • Stems may show pinkish-red color
  • 4-petaled pink flowers on a spike above water
  • Grows best in fertile, fine-textured, inorganic sediments in nutrient rich alkaline lakes
  • Prefers heavily used, highly disturbed lakes receiving nitrogen and phosphorus-laden runoff
  • High water temperatures promote multiple periods of flowering and fragmentation
  • Native to Europe, Asia, and northern Africa,arrived in WI in the 1960’s

Life History

  • Reproduces vegetatively by fragmentation and runners (stolons)
  • Produces shoot fragments 1-2 times/summer, carried downstream by water currents or boaters
  • Very poor seed germination
  • Rapid growth in spring because stolons, lower stems, and roots overwinter

Why Is It A Problem?

  • Forms dense leaf canopy shading out native aquatic plants resulting in monotypic stands
  • Disrupt predator-prey relationships by keeping out larger fish and reducing nutrient-rich native plants for waterfowl
  • Inhibits recreational uses like swimming,boating, and fishing
  • Obstruct industrial/power generation intakes
  • Cycle nutrients from sediment to water column, decreasing water quality and algae blooms
  • Can stay alive for weeks if moist

What Can Be Done?

  • Monitoring and Prevention!
  • Dispersed by boats, motors, trailers, bilges, live wells, or bait buckets
  • Check all equipment used in infested waters and remove all aquatic vegetation
  • Learn to identify and check for new colonies

Biological Control Methods

  • Eurhychiopsis lecontei, a native weevil
  • Adults feed on the stems and leaves, and females lay eggs on tip. Larvae bore into stems and cause extensive damage
  • Three generations of weevils hatch each summer, females lay up to two eggs per day

Mechanical Methods

  • All roots and fragments MUST BE removed
  • Hand-pull if <0.75 acres or <100 plants because thorough and selective
  • Mechanical cutters and harvesters are nonselective and remove beneficial aquatic plants
  • Harvesting creates fragments so only use on widespread established colonies
  • Hand cutters work best inshore
  • Bottom screens prevent new sprouts and kill grown sprouts; good for severe infestations in low boat traffic areas but are non-selective

Chemical Methods

  • Herbicide treatment not recommended because non-selective and disruptive to aquatic ecosystems

Note: DNR permits are required for chemical treatments, mechanical treatments, some manual treatments, biological control, bottom screening, and buoy/barrier placement.