Eurasian watermilfoil (Myriophyllum spicatum) is a submersed aquatic perennial. It was introduced to the U.S. from Eurasia in the 1940s as an aquarium ornamental. It is now considered one of the worst aquatic weeds, occurring in nearly every state. Watermilfoil tolerates a wide range of water conditions and often forms large infestations.
This watermilfoil grows long stems through the water column. Relatively short, branched leaves resembling feathers develop at the uppermost parts. The plants typically grow into dense mats and may develop small floral spikes that will emerge from the water.
This aquatic weed is tolerant to cold temperatures and begins to grow early in spring, sooner than native submersed plants. It forms a dense canopy along the surface and shades out the vegetation below. It is considered to have less value as a food source for waterfowl compared to native plants. Water quality is degraded by the senescence of watermilfoil. Recreational activities are hindered. Water intakes get obstructed, and decaying mats can foul lakeside beaches.
Eurasian watermilfoil reproduces by fragmentation and also by seed. Human activities can spread this invasive weed if caution is not taken to remove fragments from boats, trailers, and equipment extracted from infested waters. NC Department of Agriculture & Consumer Services has listed this species as a Class B noxious weed. It is illegal to sell or transport Myriophyllum spicatum in North Carolina.
Both biological and chemical control are used to prevent the further spread of watermilfoil infestations. Bio-control work began as early as the 1960s. Research continues the effort to find better control agents. Herbicides are moderately effective.