Non-native species: Japanese Knotweed
Issue
Japanese knotweed is native to Japan, Taiwan and China, and was introduced to Europe as an ornamental plant in the early 19th century. It is a large vigorous weed that appears to have no natural enemies in Britain. It can colonise most habitats and is regarded as a troublesome pest in many parts of the country because of its rapid invasion and domination of habitats, which results in the exclusion of other plants. It can damage property (for example by growing through tarmac or even the floors of houses) and therefore needs to be cleared from development sites. The species also causes problems in terms of flood management. It increases the risk of riverbank erosion when the dense growth of the plant dies back in the autumn exposing bare soil. It can also create a flooding hazard if the dead stems are washed into the streams and clog up the channel. A fragment of root as small as 0.8 grams can grow to form a new plant.
The New Atlas of the British and Irish Flora (published in September 2002) found that the species has increased its range considerably since the previous Atlas published in 1962.
Government Action
The Government is aware of the problems of invasive non-native plants such as Japanese knotweed. While there is no statutory requirement for landowners to remove the plant from their property, because of its potential harm to native species, it is listed on Schedule 9 and subject to section 14 of the Wildlife and Countryside Act 1981, which makes it an offence to plant, or cause this species to grow, in the wild. Both the Police and local authorities have enforcement functions for the 1981 Act. In addition, Japanese knotweed is regarded as controlled waste and has to be disposed of at licensed sites or by burning on site.
The cost of a national eradication programme using current techniques is prohibitively expensive, estimated in the Defra Review of Non-native Species Policy to be in the region of £1.56 billion. However, the Environment Agency does take local measures if flood defences are compromised (using risk assessment and local knowledge). In Cornwall, a more proactive programme has been implemented by the Agency in association with the Cornwall Knotweed Forum.
Defra is contributing £160,000 to a 4 year scientific research project (due to report in 2007), in collaboration with Cornwall County Council, the Environment Agency and others, into the biological control of Japanese knotweed. The study will undertake the necessary research to establish whether biological control is a feasible method for the long-term, sustainable management of Japanese knotweed in the UK.
The Environment Agency (in partnership with Defra and Network Rail) has published the knotweed code of practice for those involved in the development industry, which faces the problem on a large scale. Much of the advice also holds good for householders and private landowners. Page 6 sets out the relevant legislation under the Wildlife and Countryside Act 1981 and "controlled waste" issues in more detail. The code also gives practical advice on the use of herbicides and other control methods.
Background
Further information
You can get advice on managing controlled waste and the use of pesticides near water from the Environment Agency on their customer services line; 08708 506 506. If you see anyone illegally moving or disposing of controlled waste you can call their incident hotline on 0800 80 70 60.
You may also find the Environment Agency’s short factsheet on Japanese knotweed useful.
Cornwall County Council is particularly proactive in tackling the significant knotweed problem in that region. Its Japanese Knotweed pages offer advice relevant to householders and landowners anywhere in Great Britain.
Page last modified:
13 June 2008
Page published: 26 May 2005