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Parrotfeather milfoil (Myriophyllum aquaticum) is a native of South
America that grows well in Washington waters. Because of its interesting growth
habit (sticks up above the water surface) and beauty, parrotfeather is a popular
plant for aquatic gardens and is sometimes sold for aquarium use. Washington
listed parrotfeather on its quarantine list because it rapidly takes over lakes,
ponds, and ditches. Aquatic gardeners cannot legally purchase, trade, or sell
parrotfeather in Washington.
People can easily identify parrotfeather by its
bright green, stiff, feather-like foliage that can extend up to one foot above
the water's surface. It looks like tiny green fir trees growing on the water.
Because all the parrot feather plants in the United States are female, they
produce no seeds. However, the plant spreads readily through fragmentation of
the stems and rhizomes.
Parrotfeather forms dense mats of vegetation that can entirely cover the surface of the water in shallow lakes, ponds, ditches, and backwaters in rivers. The plant does not grow out into deep water, but will colonize all shallow waters. 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. We are particularly concerned about parrotfeather in rivers (such as the Chehalis and Yakima Rivers) because it may block passage for salmon and it causes pH and other water quality issues in backwater areas where juvenile salmon rear.
Parrotfeather is an especially problematic plant because it is so difficult to control. Once it gets into a waterbody, it takes tenacity to eliminate it. 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.
Parrot feather is a serious, costly pest when introduced to Washington
rivers, ponds, ditches, and lakes. Unfortunately, because of its attractiveness,
lake residents have deliberately planted this species not knowing how
invasive
and aggressive its growth could be. The Longview/Kelso Drainage District staff,
where parrotfeather is established, estimate that they spend $30,000-$40,000 per
year for control (mostly mechanical removal). Another ongoing effort is taking
place in backwaters along the Yakima River where local, tribal, and state
agencies are combining efforts to eradicate a small backwater infestation of
parrotfeather.
Parrot feather milfoil is easy to identify.
Look for:
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
Problems with this page, contact Kathy Hamel at kham461@ecy.wa.gov
Copyright © Washington State Department of Ecology. See http://www.ecy.wa.gov/copyright.html.
