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nov.
22

Invasive knotweed control videos: Fallopia or Polygonum species

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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.

*Click here* if you're interested in borrowing a knotweed injector (must reside in King County, WA). Note: borrowing is done for 2024 season and will re-open July 2025. Email us to be added to next year's to-contact list.

Introduction to knotweed

About the plant, how to identify it, and how it damages river banks.

Resources:

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.

Resources:

How to control knotweed by using herbicide injection

Learn how to inject chemical herbicide into knotweed stems using a stem injector. View the herbicide injection album on Vimeo. 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).

 

Injector-training-videos-screenshot

INJECTOR BORROWING IS CLOSED FOR THE 2024 SEASON (Available July - 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.

How to Borrow an Injector - PDF

STEP 1: Watch all the above videos on how to control knotweed by using herbicide injection

STEP 2: Take this assessment.

  • 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

BOOKING FORM (steps 3-5)

  • If you have no way to meet at any of the times provided, email us at knotweed.injectors@kingcounty.gov and we can try to accommodate your schedule as able.
  • Pick up/drop off instructions will be provided in their respective confirmation emails. 

STEP 3: Reserve an injector (10-day reservation window, can drop off sooner)

STEP 4: Schedule a time to pick up the injector at King Street Center (ideally the same day your reservation begins).

STEP 5: Schedule a time to return the injector (any available time before the end of your 10-day reservation)

STEP 6: 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.

STEP 7: You're done! Thanks for reducing the impact of knotweed in King County.

More resources:

How to control knotweed using herbicide spray

Learn how to apply chemical herbicide on knotweed using a backpack sprayer.

More resources:
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 link)
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.

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