Japanese knotweed (Polygonum cuspidatum) is a non-native invasive species that threatens our community. This rapidly growing plant is quick to shade out native species and garden cultivars. It takes over roadsides, residences and community recreation areas, threatens our stream banks and increases fire danger. While the towering stems of the plant look menacing, the real issue is the underground rhizome that can grow lightning fast and invade new areas.
Effective treatment requires a multi-pronged approach that will need more than one attack. Cutting the knotweed only removes the aboveground portion and only serves to stimulate the below ground rhizome. In some cases weekly mowing can eventually draw down enough of the plant’s reserves to kill it.
The best approach to control is through a combination of cutting and herbicide application. A late spring/early summer treatment followed by an early fall re-treatment is needed. Several years of treatment may be needed for well-established populations. The plant will not re-sprout from the cut cane, but removing them may aid in finding and treating re-sprouts in an infested patch. The area will also be more conducive to revegetation if the cut canes are removed. You will need: Loppers Herbicide (glyphosate concentrate) Rubber gloves Long pants, long sleeves, sturdy shoes- not sandals Spray bottle Liquid Dye (food colouring or Rit dye works) Glyphosate concentrate- Glyphosate is a non-restrictive use herbicide.
Anyone can purchase and use it. This does not mean that this product is not without some risk if used improperly. As it is a pesticide, you are legally required to read and follow all instructions on the label. This herbicide should not be used in the water and residue or left over chemical should not be allowed to get into public waters including household drains. Used gloves can be disposed of in the trash. Contaminated clothing should be washed separately. The herbicide is considered non-toxic to pets and humans, but as a precaution please keep them out of the area until the herbicide has soaked in.
The key to effective herbicide use is the correct dosage or percent active ingredient. Too much and you will only harm part of the plant. Too little and it has limited effect.