Japanese Knotweed (Fallopia japonica)

Species

Distribution


Japanese knotweed (Fallopia japonica)

Photo courtesy of GB Non Native Species Secretariat


To view NBN location data click here

Impacts

Pathways

  • Once established the rapid growth rate forms dense stands in both open and riparian areas that exclude native vegetation and prohibiting regeneration.
  • The monospecific stands reduce diversity and alters habitat for wildlife.
  • Can grow through tarmac and concrete (in some cases within dwellings) and therefore must be cleared completely before starting to build or lay roads.
  • Movement of plant fragments by wind or water
  • Movement of contaminated soil.
  • Plant debris on vehicles can also introduce this species to new areas.

Management

Prevention

The Environment Agency’s Advice for managing Japanese Knotweed on development sites should be followed. Where possible avoid mechanical cutting as unless properly controlled this can lead to further spread. Do not dump contaminated soil or plant fragments, dispose of them according to the Waste Management Licensing Regulations 1994. These define the licensing requirements which include “waste relevant objectives”. These require that waste is recovered or disposed of “without endangering human health and without using processes or methods which could harm the environment”. When leaving contaminated areas please check clothes, equipment and vehicles for plant fragments and/or contaminated soil.

Physical Control

Mechanical excavation of soil contaminated with Japanese Knotweed rhizome can be undertaken if time is restricted with contaminated soil being stockpiled elsewhere on site for herbicide treatment, being buried on site or being taken to a licensed Landfill site. Excavation to landfill should be considered a last resort as this is highly expensive and environmentally damaging.

Chemical Control

Can be carried out over a number of years, using herbicides such as triclopyr, picloram or glyphosate. Where the plant grows near a watercourse, the range of herbicides available for use is restricted and written permission must be obtained from SEPA . Chemical application can be through surface spraying and stem injection.

Biological Control

Using a sap-sucking psyllid insect (Aphalara itadori) is under development and is being considered for use in the UK.

Important Note

Japanese Knotweed is very vigorous and any control programme must be carefully managed. A piece of rhizome or stem material as small as a thumbnail can regenerate, and so measures must be put in place to mitigate the possibility of accidentally spreading the plant. Control must also take into account the wider environment to prevent reinvasion from likely corridors, such as fly-tipping, railway lines and watercourses. The Tweed Forum have had success in controlling Giant Hogweed (see link below).

Links

Non Native Species Secretariat identification guide

Non Native Species Secretariat Fact Sheet

SNH SAF Identification Guide

SRDP-eligible methods of control

NetRegs Guidelines

SNH SAF Training Manual

Tweed Forum Invasives Project

SEPA Guidance for Contaminated Waste

Environment Agency Guidance on Managing INNS in or near Freshwater

Invasive Species Ireland Fact Sheet, Best Practice Guidance Document and How to Manage Japanese Knotweed at Home Leaflet.

Cornwall Knotweed Forum

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