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!
- 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
- 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
- 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
- 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.