Japanese Knotweed

Asked September 17, 2020, 10:03 AM EDT

I have a line of Japanese knotweed in a meadow that is mowed annually. How far away from the line of knotweed should I stop mowing to avoid aggravation of the plant. We are having the knotweed treated chemically to eventually eliminate it, but it is still robust at this point.

Benzie County Michigan

1 Response

As with any invasive, a multi-pronged, long-term approach is needed to eradicate the plant. I am including a link below to the DNR web site which provides more information on control methods for Japanese Knotweed.
https://www.michigan.gov/documents/dnr/knotweed_BCP_372280_7.pdf

You will see that sometimes mowing/cutting is sometimes done to reduce plant size and facilitate treatment, but it is not recommended. So, look closely around your line of Knotweed and if you see any shoots coming up, then mow wider than that. Make sure the chemical application is sufficient to cover all of these shoots and not just the main plants.
One observation from my personal experience, don't assume the Knotweed is gone just because the above ground plant appears dead. The roots are very deep and it may take many growing seasons to kill the roots. For this reason, I would recommend you continue to monitor the area after treatment is completed. Watch for new shoots within a wide perimeter of the original plants and if any are observed, have them treated immediately before they grow in size. The chemical can be more effective on smaller growths.
Hope that helps and good luck!