If you are within 100 feet of a wetland (pond, ocean, stream, etc.), we can usually add you to an existing permit or help you to apply for the required permit. We then help you with every phase of the work. Please call Laura or Nan if you are near a wetland. Using herbicide in a wetland buffer zone without an approved plan is harmful to the area and is against the law. The Rockport Conservation Commission is very supportive of our efforts.
Research shows that judicious application of glyphosate herbicide according to the protocols below can eradicate large fractions of knotweed infestations each year. As knotweed weakens, it may change form dramatically into a twisted, gnarly version of its former self! As the knotweed changes form, your chosen approach will need to evolve.
The herbicide glyphosate is applied in late August or early September, as near to flowering as possible when knotweed is most vulnerable and the herbicide is pulled down into the roots. It is much less effective if applied earlier in the year.
Mechanical methods without herbicide are most effective with small infestations of 50 stems or less where the infestation can be followed carefully. Mechanical control consists of cutting knotweed to approximately six inches high at least four times per growing season from June to October. All cuttings and fragments must be removed from the site and destroyed.
However, the literature and our own research have shown that repeatedly cut knotweed responds by producing more small stems over a much wider area, so cutting alone should not be undertaken unless the area can be followed for many years. Cutting without removing all fragments will spread the infestation since each piece can start a new plant.
The root clusters of knotweed at the surface may be dug up, bagged and destroyed to further discourage the plant. This is combined with the planting of native grasses and other species approved to prevent erosion and inhibit the growth of knotweed.
King County [WA State] Noxious Weed Control http://your.kingcounty.gov/dnrp/library/water-and-land/weeds/BMPs/Knotweed-Control.pdf
Montana State University Extension Service: https://store.msuextension.org/Products/Biology-Ecology-and-Management-of-the-Knotweed-Complex-EB0196__EB0196.aspx