Invasive knotweed control video
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.
For information on how to borrow a stem injector, scroll down to Resources below How to control knotweed by using herbicide injection.
Introduction to knotweed
About the plant, how to identify it, and how it damages river banks.
- 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.
How to control knotweed by using herbicide injection
Learn how to inject chemical herbicide into knotweed stems using an injection gun.
- Quiz to use and to borrow a knotweed stem injector
- How to borrow a stem injector (pdf, 92 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
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)
- Invasive knotweed
- Noxious weed best management practices
- Water and Land Resources Division multimedia
- Agriculture in King County, Washington
- Northwest yard and garden
- Animals, plants and habitat
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.