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Updated 03/14/05

picture of a patch of purple loosestrifePurple Loosestrife
(Lythrum salicaria)

Purple Loosestrife Control in Washington State

Purple loosestrife is semi-aquatic weed that is found in virtually every county in Washington State and every state in the United States picture of Purple loosestrife on a river bank except for Florida. Purple loosestrife infests environmentally sensitive habitats such as meadows, marshes, streams and river-banks, and lake shores as well as irrigation ditches, drainage ditches, and storm-water retention basins. Loosestrife harms wetlands by crowding out native wetland plants and by eliminating nutritional food sources and shelter for wetland wildlife that has adapted to specific plant communities. Loosestrife also chokes out both natural and artificial waterways, slowing natural flows and promoting deposit of silt. This process causes long-term water quality degradation and requires costly maintenance including dredging and cleaning of drainage and irrigation ditches.

Purple loosestrife flourishes in many parts of our state due in part to the relative lack of natural enemies. Loosestrife is also a prolific seed producer as individual plants are capable of producing over a million seeds. The seeds are very small, about the size of ground pepper, and are easily transported by water, wind, wildlife, boats, boat trailers and vehicles. When conditions are right, a small isolated cluster of loosestrife plants can spread and cover a marsh in one growing season, spelling a quiet death for wetlands as a natural ecosystem.

Complete eradication of purple loosestrife from Washington State is not possible at this time due largely to the extent of the infestation and the limited control options currently available. The availability of a selective herbicide approved for use in wetland areas would facilitate control efforts. Currently herbicide control options are limited to Rodeo®, which is relatively non-selective, and 2,4-D which is selective but only approved by the Department of Ecology for use in very limited instances.