Eurasian watermilfoil is a rooted, submerged aquatic plant. The leaves appear green while the stems are white to reddish.
Leaves and Stem
Leaves are feather-like, with four leaves arranged in a whorl (radiating out from a single point) around the stem. Space between whorls along the stem can be a half inch or greater. Each leaf has a central axis with 12 to 21 leaflet pairs. Leaflets are limp when the plant is removed from the water. The stem is typically light brown, but sometimes pink. Tips of the plant are sometimes red or pink in color. Color alone should not be used for identification as it can be highly variable.
A small pink flower spike up to four inches long produces tiny yellow flowers. Male and female flowers are found on the same plant.
Even though each plant can produce approximately 100 seeds per season, this species is more successful at reproducing via fragments.
Roots are thin, white, and sometimes form dense clumps underneath the plant.
Eurasian watermilfoil is a perennial that flowers twice a year, usually in mid-June and late-July. It can grow up to 20 feet tall, but typically only grows three to nine feet tall. It creates canopy-like structures as it grows toward the water’s surface. It primarily establishes through vegetative fragmentation—a fragment can break off, settle in the sediment, grow roots, and establish a new plant. The plant dies back in the fall, but the root system can survive the winter and begin growing again in the spring.
Origin and Spread
Eurasian watermilfoil is native to Europe and Asia. It was discovered in the eastern United States in the early 1900s. The species was likely introduced and spread through the movement of watercraft and water-related equipment with attached vegetation. In Minnesota, it was first recorded in Lake Minnetonka (Hennepin county) in 1987. Refer to the infested waters list for current distribution.
Don't be fooled by these look-alikes
Eurasian watermilfoil looks similar to many native, beneficial watermilfoils found in Minnesota lakes and rivers. Its common native look-alike is northern watermilfoil. In comparison, northern watermilfoil has only five to nine leaflet pairs, the space between whorls is short, and it produces winter buds (dense club-like clusters of leaves at the end of the stem) at the end of the growing season.
Eurasian and northern watermilfoils often hybridize. Hybrids have similar characteristics and may require genetic screening to distinguish from non-hybrids.
Eurasian watermilfoil (Myriophyllum spicatum) and its hybrids are prohibited invasive species in Minnesota, which means it is unlawful (a misdemeanor) to possess, import, purchase, transport or introduce these species except under a permit for disposal, control, research or education.
Threat to Minnesota Waters
Eurasian watermilfoil causes recreational, economic and ecological damage—changing how residents and visitors use and enjoy Minnesota waters.
Eurasian watermilfoil impacts:
- Dense mats at the water’s surface inhibit water recreationists.
- Overtakes habitat and outcompetes native aquatic plants, potentially lowering diversity.
- Provides unsuitable shelter, food, and nesting habitat for native animals.
What you should do
People spread Eurasian watermilfoil primarily through the movement of water-related equipment. Plant fragments can get tangled on boats, trailers, motors, anchors and other water-related equipment. All it takes is a single plant fragment to start a new population.
Whether or not a lake is listed as infested, Minnesota law requires water recreationists to:
- Clean watercraft of all aquatic plants and prohibited invasive species.
- Drain all water by removing drain plugs and keeping them out during transport.
- Dispose of unwanted bait in the trash.
- Dry docks, lifts, swim rafts and other equipment for at least 21 days before placing equipment into another water body.
Management of invasive aquatic plants involving either mechanical removal of plants or application of herbicides to public waters requires a permit from the DNR. Talk to a DNR specialist for more information.
Mechanical control can be done by cutting or pulling the plant by hand or with equipment such as rakes or cutting blades.
Herbicide control can be done using two systemic herbicides (2,4-D and triclopyr) and two contact herbicides (endothall and diquat). Systemic herbicides are taken up within plants killing the leaves, stems, and roots. Contact herbicides damage or kill only the parts of plants with which they come into contact.
Biological control involving a native insect (weevil) is currently being researched.