Japanese Knotweed Features

  • Tall herbaceous perennial with distinctive bamboo like stem.
  • Plants emerge in spring usually April time and grow rapidly.
  • Dense stands smoother out native vegetation and can make an area of land unusable.
  • Stems and rhizomes can grow through concrete, drains, roads and pavements causing structural damage.
  • Japanese Knotweed reproduces only from fragments of stem and root, not from seed. It is therefore essential that those involved in Knotweed control take great care to prevent cutting or breaking plant stems or roots.
  • It is an offence under the Wildlife and Natural Environment Act 2011 to plant or otherwise cause Japanese knotweed to grow in the wild.
Japanese Knotweed

Japanese Knotweed shoots

Japanese Knotweed

Japanese Knotweed deadwood

Japanese Knotweed

Japanese Knotweed spread

Recommended methods of control.

There are only two control methods suitable for use in a riparian situation.

  • Spraying JKSpraying 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 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 absorbed through the leaves and translocated to the roots killing the plant from the ground up.  On-going monitoring of treated stands is essential as this weed can be extremely persistent and difficult to kill. It is likely that more than one year’s treatment will be required, three years is the minimum length of control for some stands of JK.
  • stem injection gunStem 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.  Each cane gets a concentrated dose of herbicide injected below the third node.  It is most suitable for use in small stands of the plant as it is very time consuming.

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.

Any person spraying herbicide near a water course must have a PA6AW certificate.  This is the minimum qualification required to carry out this task. (Training available through the Carrick Project for interested volunteers)  Applications to SEPA in the form of a SEARS licence must also be completed to ensure permission is in place to use herbicide near watercourses. (SEARS applications will be completed by the project officer for the life span of the Carrick Project).

Download Poster here (pdf): Japanese Knotweed Poster

Japanese Knotweed