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Updated 09/10/09

Knotweed Eradication

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Reports
Integrated Management Plan

Invasive Knotweeds in Washington State: Japanese knotweed (Polygonum cuspidatum), Giant knotweed (Polygonum sachalinense), Bohemian knotweed (Polygonum bohemicum), Himalayan knotweed (Polygonum polystacyum)

Originally introduced as garden ornamentals, knotweed species are a threat to

Washington State waterways. The plant will grow in most habitats, but the most common route of spread is along stream corridors. The plant is structured similar to bamboo, and when washed away from the stream bank each node on the stem can produce a mature plant.

The plants also reproduce through the production of seeds and underground shoots. They eventually out compete the native species and create monocultures that obstruct access to riparian areas for wildlife and recreationists. Knotweed can even compete with many tree species, including streamside trees such as cottonwood and alder. The result of this alteration of species content, besides reducing access, has also been tentatively linked to the reduction of anadramous fish habitat.

The combination, of the plant's prolific ability to reproduce and the lack of natural enemies, means that knotweed threatens to encompass large areas of Washington State. A pilot control project was conducted in the southwest portion of the state in 2004 and the Washington State Dept. of Agriculture plans for the program to expand statewide in 2005.

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Reports

Integrated Management Plan

2005 Integrated Knotweed Management Plan

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Related Items

Pesticide Application Record

Evaluation of Knotweed Control Projects in SW WA