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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.
Injector borrowing is closed for the 2024 season (available July through October to King County residents
The King County Noxious Weed Control Program is piloting a new process to lend out knotweed injectors to the public. Please be patient as we test out this new system. There will be an option to provide feedback on the survey. Please note that the window to control knotweed with injectors is July to early October. Injectors can be borrowed in 10-day increments.
Injector borrowing is done for 2024, if you wish to be added to the 2025 list - email us at noxious.weeds@kingcounty.gov and we will add you to the list of folks we will email as soon as the program is back for the 2025 season.
Introduction to knotweed
About the plant, how to identify it, and how it damages river banks.
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 a stem injector. Injectors are available at a variety of sites online. If you're a King County resident interested in borrowing an injector for free from the King County Noxious Weed Control Program, please see next section (below).
Watch this series of videos about herbicide injection
How to borrow an herbicide injector
Herbicide injectors are available to King County residents from August to October.
The King County Noxious Weed Control Program is piloting a new process to lend out knotweed injectors to the public. Please be patient as we test out this new system. There will be an option to provide feedback on the survey. Please note that the window to control knotweed with injectors is August to early October. Injectors can be borrowed in 10-day increments. Follow the steps below to borrow an injector for the 2024 season.
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Watch videos
Watch the videos on this page and the series on Vimeo about how to control knotweed by using herbicide injection.
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Take the assessment quiz
- At the end of the assessment there will be a link to the booking form. If not booking immediately, please save this link. If you lose the booking form, you can take the quiz again or email us at knotweed.injectors@kingcounty.gov.
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Reserve an injector
- 10-day reservation window
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Schedule a time to pick up the injector
Pick up injectors at King Street Center.
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Schedule a time to return the injector
Pick an available time beofre the end of your 10-day reservation. Return injectors to the King Street Center.
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Fill out the survey in your confirmation email
After using the injector, be sure to return it at the time you chose in step 5, and please fill out the survey in your confirmation email. Doing so allows us to keep this service free to the public and helps us keep the injectors maintained and ready for use.
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All done
Thank you for reducing the impact of knotweed in King County.
Control knotweed using herbicide spray
Learn how to apply chemical herbicide on knotweed using a backpack sprayer.