Eurasian watermilfoil (Myriophyllum spicatum L. ) is a submerged aquatic plant native to Eurasia and northern Africa. It has the ability to overwinter and grow rapidly in the spring, blocking out sunlight needed by native plants. It impairs the ability of some fish to spawn and is not a valuable habitat for larger fish species.
Occupies water 3 – 12’ deep, growing best in fertile, fine texture, inorganic sediments. Prefers highly disturbed lake beds, heavily used lakes and lakes receiving nitrogen- and phosphorus-laden runoff. Also found in ponds, slow-moving streams, reservoirs, and estuaries. It is not successful in undisturbed areas where native plants are well established.
Leaves: submerged, feathery, limp when out of the water, 4 – 5 leaves whorl around the stem at each node. Typically uniform in diameter consists of more than 12 thread-like pairs of leaflets that resemble bones on a fish spine.
Flowers: tiny, inconspicuous, and located in the axils of flower bracts, either four petals or without. Flower spike rises 2 – 4” above the water surface.
Fruit: globoid-ovoid in shape measuring 2 mm. Long with 4 lateral lobes; these lobes are smooth, except along their margins, where they may be slightly warty. Each fruit divides into 4 chunky 3-sided seeds.
Stem: slender, thickened below the flower, doubles in width further down the stem, becomes leafless near the base. Usually, 3 -10’ long but can reach 33’ in length. Often branch repeatedly at the water’s surface.
Reproduction: primarily by fragmentation due to boating and wave action. Fragments stay alive for weeks if kept moist. They also reproduce by runners. Therefore, it is important to Clean, Drain, Dry all watercraft before entering and leaving a body of water.
Physical Control: Hand-pulling is the best method for small infestations. Raking is also an option. All plant fragments must be removed from the water and shoreline to prevent spreading the infestation. Bottom barrios (sheets of materials, attached to a lake bottom) can be used locally around docks by preventing plant growth by blocking sunlight.
Chemical Control: 2,4-D and Fluridone are the most commonly used chemicals to control this species. However, both of these have mixed results and can affect native plant populations. Permits are required for chemical applications in aquatic and sensitive habitats; always follow chemical instructions.
Biological control: Researchers have found a native North American weevil that feeds on Eurasian water-milfoil, but this method also has mixed results. Contact local DEC for more information.
Photo Credits: Title photo, Huron Watershed Counsel, http://www.hrwc.org/category/invasive-species/page/2/.Leaves photo:Lake George Association, http://www.lakegeorgeassociation.org/what-we-do/Invasive-Species/Eurasian-Watermilfoil.asp. Flower photo: Sydney Weed Committee,http://sydneyweeds.org.au/weed/eurasian-water-milfoil/./Fruit photo:USDA,http://plants.usda.gov/java/largeImage?imageID=mysp2_004_ahp.tif. Stem photo: Early Detection & Distribution Center, http://www.eddmaps.org/ontario/distribution/point.cfm?id=3908281.