Eliminating Japanese Knotweed

    Japanese knotweed is not only invasive, it’s also one of the toughest weeds to eradicate. So, what’s the best way for you to eliminate this destructive plant from your landscape?

    We spoke with Randy Prostak of the UMass Extension Landscape, Nursery and Urban Forestry Program, who advocated for applying a foliar spray when Japanese knotweed is in bloom. According to Prostak, now is the best time to spray with Bonide KleenUp, a 40% solution of glyphosate, mixed at a rate of 3 ounces per gallon. This process has a +90% control rate. After the foliar spray is applied, leave the weed alone to allow the chemical to be fully absorbed into the plant.

    It’s important to remember that glyphosate is not selective, meaning it will damage and most likely kill any plant that it comes in contact with the foliage of. If you’re spraying in an area that contains desirable plants, we recommend protecting those plants by either isolating the Japanese knotweed with cardboard, or by applying the mixed solution directly to the weed with a brush or Red Weeder applicator stick.

    Once winter has come and gone and spring is back, crush the stalks, dead or alive, and wait for any persistent plants to flower before applying the foliar spray again.

    Completely eliminating Japanese knotweed from the landscape is a process that involves annual spraying, but if you stick to the plan you can eliminate this invasive weed and keep it from choking out desirable plants in your garden. Remember, our knowledgeable staff is always here to help and answer any questions you may have.


    Photos courtesy of the UMass Extension Landscape, Nursery and Urban Forestry Program

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