Japanese Knotweed is listed under Schedule 9 of the Wildlife and Countryside Act (1981) making it an offence plant or allow colonisation in the wild. Japanese knotweed is a very difficult plant to control and can cost over £1,000 to per square metre to remove from constructions sites, requiring disposal of contaminated material and topsoil as controlled waste under the Environmental Protection Act (1990). There are a variety of methods used to control Japanese knotweed including herbicide treatments, uprooting and removing infested soils, stem injection and root barriers.
If you locate Japanese Knotweed notify the appropriate conservation body or authority such as the Wildlife Trust, RSPB, Non-native Species Secretariat, NBN Gateway, Environment Agency, The Biological Records Centre, Natural England or Local Authority. These organisations will be able to give advice on how to remove and control the spread of Japanese Knotweed.
Photo: Japanese Knotweed alongside a canal (Photo by Roger Kidd - Geograph)
For more information regarding the control of Japanese Knotweed see the Environment Agency's guidlines for Japanese Knotweed: Managing on Development Sites.
You should record the presence of invasive species on a national database. You can record online at the Non-native Species Secretariat website. You should also alert the appropriate land owner, council and or management body to the presence and location of this plant.