Aquatic Invasive Species

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Eurasian watermilfoil
(Myriophyllum spicatum)

Photo Credit: Alison Fox,
University of Florida, Bugwood.org

Eurasian Watermilfoil is a submersed, perennial herb. It produces an extensive, shallow root system in water sediment that is capable of generating new shoots. It grows stems and branches that are 1 to 20 feet long with the average size from 6 to 8 feet. The branched stems produce four leaves at each node, but are leafless at the base. The nearer stem grows to the water surface and the internodes branch and leaf development occurs. Heavy infestations form impenetrable mats of stems and leaves form below the water's surface. The stem tips are tassel-like and reddish early in the season. The feather-like, pinnate leaves have 14 or more pairs of leaflets and are around 1-inch long. White to pinkish flowers are produced by mid-season in coils on spikes above the water. The flower stalk may bend parallel to the surface of the water. Eurasian watermilfoil reproduces by seed from buds, stem fragments, rhizomes and root crown as the stem dies back each season.

Eurasian watermilfoil inhabits lakes, reservoirs, ponds, streams and ditches where standing or slow moving water occurs. It is very competitive with native species and can completely dominate a plant community within a few years of introduction. Because of the plant's ability to form dense growths, water use activities become severely impaired.

Management steps include boat, vehicle and equipment cleaning and inspections to prevent its introduction. Water flow and wave action prevents its establishment. Mechanical removal and mowing of the stem spreads this weed but physical removal of the root system is effective. Herbicides are available.

Eurasian Watermilfoil infestation. Photo Credit: Leslie J. Mehrhoff,
University of Connecticut, Bugwood.org

Related Links

100th Meridian Initiative
California Department of Fish and Game
Protect Your Waters
Tahoe Resource Conservation District - Aquatic Invasives

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