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Noxious weeds

King County, Washington

To offer a suggestion or report an error on the King County Noxious Weeds website, please contact Sasha Shaw, education specialist.

Invasive knotweed control videos

Learn how to identify invasive knotweed, understand how it damages native plant communities and streambanks, and find out how to control it using manual methods and injecting or spraying chemical herbicides.Windows Media Player (external link) is needed to watch these videos.

Introduction to knotweed
About the plant, how to identify it, and how it damages river banks. 3 min. 45 sec.

Learn more about knotweed identification, biology and impacts.

Take a free class on knotweed control and borrow a stem injector.

How to control knotweed without chemicals
Learn about digging out this invasive weed, cutting and starving roots, and cutting, covering and shading roots as control methods. 6 min. 44 sec.

Learn more about shovels or hand-cutting tools or plastic mulching materials (external links)

How to control knotweed by using herbicide injection
Learn how to inject chemical herbicide into knotweed stems using an injection gun. - 11 min. 41 sec.

How to borrow a stem injector (pdf, 13 Kb)
Email us for more info on borrowing a knotweed stem injector
Purchase a stem injection gun/tool (external link)
Read about herbicides labeled for use with stem injection method (external link)

How to control knotweed using herbicide spray, 2 min. 35 sec.
Learn how to apply chemical herbicide on knotweed using a backpack sprayer.


Get more information on using herbicides to control knotweed
Learn about choosing and calibrating a backpack sprayer (external link)
Find out about pesticide license requirements in Washington State (external lnk)
Apply for a permit to apply aquatic herbicides in Washington State (external link)

Related information

Related agencies

Program offices are located at 201 S. Jackson St., Suite 600, Seattle, WA 98104. To contact a staff member at the King County Noxious Weed Control Program, please call 206-477-9333 or by reach them by email.