Invasive Weeds Management
Japanese Knotweed. (JK)
Recommended methods of control.
There are only two control methods suitable for use in a riparian situation.
- Spraying using knapsack sprayer and systemic, glyphosate based herbicide. Roundup Pro Biactive is widely accepted as the most effective chemical suitable for use near watercourses.
Timing of spraying is important with the best results achieved during autumn when the plant has developed flowers. Both the top and underside of the leaves should be sprayed before the plant starts to die back for winter. The weed killer is translocated to the roots killing the plant from the ground up. Any re-growth the following Spring should be treated using the same methods. Ongoing monitoring of treated stands is essential as this weed can be extremely persistent and difficult to kill. In all instances, it is likely that more than one application of glyphosate will be required to kill the plant however the impact and biomass of the plant can quickly be reduced using the described methods.
- Stem Injection is a relatively new technique that is proving to be highly effective in destroying JK. It relies on specialist equipment to inject a measured dose of herbicide into individual JK canes. It is most suitable for use in small stands of the plant.
Under no circumstances is cutting or strimming JK recommended as this only serves to spread the plant. This method also raises the problem of dealing with the cut material which becomes a controlled waste and must be sent to a licensed landfill facility willing to accept this waste. Leaving the cut material to decompose in situ is not acceptable as it can re-grow thereby increasing the problem.