City of Seattle, Seattle Public Utilities, Knotweed Control 2010-current, Cedar River Municipal Watershed, King County, WA

The City of Seattle’s Cedar River Municipal Watershed is managed to support and supply clean drinking water to the greater Seattle area. The watershed covers 91,000 acres, hosts a rich diversity of plants, animals, and habitats, and is owned by the City of Seattle. In 1999, the noxious weed knotweed was detected in the watershed and control was limited to manual and mechanical methods due to an herbicide moratorium intended to prevent broadcast spraying of roadside vegetation. These manual control methods were largely unsuccessful and impractical for controlling acres of knotweed growing in remote locations of the watershed. In 2010, Seattle Public Utilities passed the first ordinance through Seattle City Council to approve the limited use of imazapyr to control knotweed in the watershed for three years. Successive knotweed ordinances have been passed, allowing for herbicide control of knotweed in the watershed from 2010-current. The reports included in this package are provided to Seattle City Council annually as a requirement of the ordinance. The data table provides the control history since the passage of the first ordinance and includes information about patch size and amount of imazapyr used. This data package will be updated annually with ongoing control efforts.