Contact Snohomish County to reserve a knotweed stem-injector to control small knotweed patches in an upland area (see sidebar).
Be patient and wait until the knotweed is large enough; is producing flowers, or after it has bloomed. This could involve resisting the urge to cut or mow knotweed. The best timing is between August to first frost, as long as the leaves are not yellow.
Knotweed stems need to be at least ½ inch wide. You need to provide your own herbicide. Use undiluted herbicide which has glyphosate as an active ingredient. It is widely sold under different brand names.
Contact us for advice if knotweed is growing near water, or is in a wetland.
Coordinator
Ph: 425-388-7548,
Cell: 425-238-0367
Fax: 425-388-7538
1111 Washington St.
P.O. Box 42560
Olympia, WA 98504
Phone: 360-902-2053
Before attempting to control knotweed located in or near the road right-of-way, contact Snohomish County Noxious Weed Control Program: 425-388-7548 or email Geraldine Saw.