Knotweed Control
Public Works | Natural Resources Division
Knotweed
Knotweed species (Fallopia spp.) are aggressive perennial species native to Asia. Knotweed is a Class B species that isn’t required for control in Skagit County due to its large distribution but is on the state quarantine list.
Knotweed species are very aggressive, capable of forming large dense stands, crowding out native vegetation, and degrading wildlife habitat. Often found in riparian areas, waste sites, gardens, and roadsides, it spreads easily via root/stem fragments. Knotweed does the most damage in riparian systems, as it degrades salmon habitat and water quality.
How We Treat Knotweed
Our knotweed grant program focuses primarily on Samish River and Grandy Creek, where we’ve been treating knotweed since 2013. Knotweed populations on Grandy Creek have been steadily declining, so our focus has shifted to the portion of the Samish River system that lies east of Old Highway 99.
When working with knotweed species in a water system, we take a top-down approach. This ensures treated areas downstream aren’t at risk of being recolonized by upstream populations. We spray knotweed with herbicide at close range to make sure we are using as little as possible and that is has the smallest possible impact on other plants.
Partners
We coordinate our knotweed treatment efforts with Skagit Cooperative Management Area Group, which includes the Washington Department of Fish and Wildlife, the Washington State Department of Natural Resources, North Cascades National Park (as governed by the National Park Service, US Department of the Interior), Skagit Fisheries Enhancement Group, Skagit Land Trust, Seattle City Light, Snohomish County Noxious Weed Control Board, Whatcom County Noxious Weed Control Board, the Nature Conservancy, and the Samish Indian Tribe.
