Eurasian Watermilfoil

Myriophyllum spicatum

eurasian watermilfoil
 Image credit: Allison Fox, University of Florida

Characteristics

Eurasian watermilfoil, a submerged aquatic in the Haloragaceae family, is an invasive that prefers stagnant to slow moving water. It can be easy to misidentify native milfoil species as invasive due to their close resemblance to their Eurasian counterparts. So, some of the key characteristics you should look for when suspecting Eurasian watermilfoil (EWM) lie within the plant's leaves:

  • whorls (circles) of four delicate feather-like leaves around its stem, and usually 12-21 leaflet pairs per leaf as opposed to native northern watermilfoil which has more rigid leaves with only 5-10 leaflet pairs per leaf. 
  • notice the often bright green color distinct to the EWM  
  • rooted in lake or river bottoms, their stems will grow toward the water surface, usually reaching lengths of 3-10 feet
  • EWM collapses when pulled from water, while native milfoil maintains structural integrity out of water
  • forms dense mats which restrict light availability for native species

As mentioned, EWM prefers stagnant to slow moving water, thus you’ll often find it invading ponds, lakes, and/or slow moving streams. 

For more information visit MISIN. 

 

KISMA Management Practices

Unfortunately, Eurasian watermilfoil is already established within the Keweenaw and the majority of the continental United States. It has been detected within the Keweenaw waterway, and cases have even been reported on Isle Royale. Management of EWM is heavily dependent on early detection and prevention because once it takes hold on a site, it can be incredibly difficult to extirpate. New colonies often appear near boat landings or other disturbed sites, and hand pulling or raking is an effective way to remove these smaller patches. However, once a body of water is taken over by EWM, not much can be done outside of widespread chemical treatment or bottom screening, both of which require permits and can damage native species. In order to prevent these infestations, make sure to follow these state mandated steps when traveling between waterways in the Keweenaw:

  1. clean boats, trailers, and equipment of any visible plant fragments
  2. drain ballasts or any other water from boats, trailers, and equipment
  3. dry boats, trailers, and equipment 
  4. learn how to identify EWM, and monitor access sites, marinas, or inlets for the first sign of invasion

Note: Eurasian watermilfoil can spread via fragments, so even one small stem fragment can take root and form a whole new colony. It is crucial that all plant matter is removed before you travel from waterway to waterway.

 

ewm leaves

(image credit: Graves Lovell, Alabama Department of Conservation and Natural Resources) feather-like leaves of Eurasian watermilfoil 

ewm underwater

(image credit: Robert Johnson, Cornell University) a view of EWM underwater 

mat of EWM
(image credit: Leslie J. Mehrhoff) a dense mat of EWM 
ewm on boat

(image credit: Tip of the Mitt Watershed Council) EWM can easily hitch-hike on watercraft 

Sources

"Eurasian watermilfoil (Myriophyllum spicatum)." MISIN, 2020.

"Eurasian watermilfoil." Tip of the Mitt Watershed Council, 2021.

"Leslie J. Mehrhoff." bugwood.org

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