Parrotfeather (Myriophyllum aquaticum) - A Noxious Aquatic Weed in Washington

General Information about Parrotfeather (Myriophyllum aquaticum)

Parrotfeather milfoil (Myriophyllum aquaticum) is a beautiful looking plant that was sold mostly for aquatic gardens, but was sometimes also sold for aquarium use. Since 1996 parrot feather has not been legally offered for sale in Washington because it is an aggressive invader that rapidly takes over lakes and ponds. Parrotfeather is readily identified by its bright green, stiff, feather-like foliage that can extend up to one foot above the water's surface. Like Brazilian elodea, parrotfeather is a native of South America that grows well in Washington waters (follow this link to see where parrotfeather is located in Washington). All the parrot feather plants in the United States are female, so no seeds are produced. However, the plant spreads readily through fragmentation of the stems and rhizomes.

Growth Habit

Parrotfeather forms dense mats of vegetation that can entirely cover the surface of the water in shallow lakes. The tough stems make it difficult to boat, swim, fish, or water ski. It provides ideal habitat for mosquito larvae and the mass of the plant can cause flooding to occur. Parrotfeather is an especially problematic plant because it is so difficult to control. Once it gets into a waterbody, it is nearly impossible to eliminate. Parrotfeather's underwater and above water foliage makes herbicides difficult to deliver effectively, and the emergent leaves and stems are covered in a waxy cuticle that inhibits herbicide uptake. Plant-eating sterile grass carp find parrotfeather unpalatable due to the tough, woody stems and high tannin content of the plants. Harvesting and other mechanical controls produce fragments that help spread the plant.

Management

Where parrot feather is well-established in the Longview/Kelso drainage ditches in southwestern Washington, the diking district staff estimate that they spend $30,000-$40,000 per year for control (mostly mechanical removal). Parrot feather is a serious, costly pest when introduced to Washington rivers and lakes. Unfortunately, because of its attractiveness, lake residents have deliberately planted this species not knowing how invasive and aggressive its growth could be.

Identification

Parrot feather milfoil is easy to identify. Look for:

Bright green, "fir-tree-like" emergent leaves and stems.
Leaflets arranged in whorls (4-6) around the stem.
Each leaflet has a feather-like pattern.
Dense mat of intertwined brownish stems (rhizomes) in the water.
Reddish, feathery-leaved, limp, underwater leaves may be present.

Although they are both in the same genus and closely related, Eurasian watermilfoil doesn't have above water leaves.

Follow This Link for Technical Information about Parrotfeather

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