Japanese knotweed infestations can be controlled and eliminated through a variety of methods. Depending on factors such as timescale, location of infestation and its surrounding environment the method can vary but through correct application and management Japanese knotweed growth can be stopped and prevented from returning. The main methods of control are:
Chemical – Qualified and competent personnel are permitted to use herbicides to control and eliminate Japanese knotweed. The application method and specific chemical used will depend on factors such as the infestations proximity to watercourses and local wildlife.
Burial – If time is a factor and it is unfeasible to wait for the numerous growing seasons that herbicide treatment may take to eradicate an infestation Japanese knotweed can be excavated and buried on site. All material contaminated with Japanese knotweed is encased in a root barrier membrane that prevents further growth and buried at a depth greater than 5m below the surface to prevent the material being disturbed and re-infesting the area.
Bund – If burial on site is not an option a bund can be created by designating an area of the site to place all material and soil contaminated with Japanese knotweed. The bund is then treated with herbicide allowing the original area of infestation to be developed or managed without the presence of Japanese knotweed being an issue. This method can be applied if there is sufficient time and space to relocate contaminated material and treat it on site, preventing the high costs of disposing Japanese knotweed at a licensed waste management facility off site.
Cutting – Japanese knotweed stems can be cut and dried out however this will only address the growth above ground and will take many years to effectively control the infestation without the use of chemicals or digging out the Japanese knotweed rhizome.
Burning – As with cutting this method can be ineffective without excavating Japanese knotweed rhizome from the soil and burning it with all plant material.
Biological Control – After careful research and development, tiny plant-eating insects called psyllids have been identified as a possible means to control Japanese knotweed, with tests being done to establish whether to release them nationwide. The ‘knotweed bugs’ have been released in some parts of England as part of a trial. Although they may control the Japanese knotweed they will not eradicate it fully otherwise the bugs would have nothing left to eat and they would die.