UK: New Advice On A Horticultural Invader

Last Updated: 13 September 2007
Article by Emma Humphreys and Peter McKeon

Originally published in Estates Gazette

Japanese knotweed can create havoc for developers. Peter McKeon and Emma Humphreys report on the latest code from the Environment Agency.

Recent reports have indicated that the cost of dealing with Japanese knotweed on the Olympic site in east London could be around £70m.

Outside its native areas of Japan, Taiwan and northern China, Japanese knotweed is a highly invasive weed. It was introduced into the UK for use as an ornamental plant and to help stabilise embankments in the 1800s. It subsequently became naturalised. It can grow in almost any habitat and is now found in almost every county in the UK, particularly along rivers and railways and on brownfield sites.

The plant is an increasing problem for many developers, which, until recently, have been given little clear guidance on dealing with it or on their potential liabilities for failing to do so. However, The Knotweed Code of Practice: Managing Japanese Knotweed on development sites (the code), which was produced by the Environment Agency towards the end of 2006, provides significantly more advice.

Japanese knotweed shoots can push through tarmac and damage pavements and building foundations. The presence of the plant on a development site can lead to significant delays and huge costs. For example, effective control of the plant using herbicides takes at least three years. Excavation offers rapid removal, but the costs are substantial; the disposal at a licensed landfill site of a stand of Japanese knotweed measuring 1m2 will cost in the region of £27,000.

A developer that has Japanese knotweed on its site also faces the risk of criminal and civil liability. Under the Wildlife and Countryside Act 1981, for example, it is an offence to plant or otherwise cause the species to grow in the wild. Japanese knotweed is also classed as controlled waste under the Environmental Protection Act 1990 and must therefore be disposed of safely at a licensed landfill site, according to the Environmental Protection Act (Duty of Care) Regulations 1991. (See also EG22 October 2005, pp226-228.)

Old and new codes of practice

In 2001, in response to the spread of Japanese knotweed, the Environment Agency published the Code of Practice for the Management, Destruction and Disposal of Japanese Knotweed. This provided an outline of the main techniques for the disposal and treatment of the plant, such as burning and burial, off-site disposal and herbicidal treatments. The legal implications of mismanaging Japanese knotweed were mentioned, but there was little clarification of the likely interpretation and application of the relevant legislation by the Environment Agency and others.

Since the publication of this first code, awareness of the problems caused by Japanese knotweed has increased, particularly among developers, local authorities and environmental professionals. This has triggered a growth in the number of companies specialising in Japanese knotweed control and the techniques developed to deal with it. However, this flurry of new companies and techniques has left many developers uncertain as to which techniques can be trusted to secure sites from potentially serious problems and the extent of their responsibility to do so.

Partly because of these concerns, the Environment Agency decided to revise its code. The new code is much more detailed than its predecessor and has been designed to be more user-friendly.

Identification and control

The code offers advice on how to identify Japanese knotweed, and, to that end, includes photographs of its distinctive features. Appendix III provides details of other plants that are commonly found on development sites and that can be confused with Japanese knotweed.

The information provided in the code on the control and management of Japanese knotweed is more detailed than that of its predecessor. In particular, it makes it clear that disposing of the plant off-site should be regarded as a last resort. The code also states that treated soil that is free from Japanese knotweed can be reused only on-site; such soil can be removed only if it is to be disposed of at a licensed landfill.

A wider range of management techniques is discussed, including the installation of a root-barrier membrane, and a flowchart sets out appropriate control techniques. The code offers more practical advice for developers. For example, several local authorities now insist upon receiving a Japanese knotweed management plan prior to the start of control works, and the appendices to the code provide a template for such a plan. The code states that the plan should be overseen by a clerk of works and all relevant contractors should be made aware of its importance. A brief "tips for developers" section is also included.

The legislation relating to the management and disposal of Japanese knotweed is set out in greater detail. This includes useful guidance concerning section 14 of the 1981 Act, which makes it an offence to plant or otherwise cause to grow Japanese knotweed in the wild. The code states that it is not an offence to have Japanese knotweed on land, indicating that a failure to deal with it is not akin to causing it to grow. However, it points out the possible risk of a civil nuisance claim should the plant escape onto neighbouring property.

The role of the Environment Agency in the management of Japanese knotweed has been clarified. The code indicates that the agency’s priority is to regulate waste, and it is unlikely to take action under the 1981 Act unless a waste offence has also been committed, although other organisations may choose to do so.

Implications of the new code

Any revised code on Japanese knotweed would have needed to provide more detailed guidance, given the development of a wider range of control techniques. However, the new guidance is not without its problems; several of the changes to the code, in particular the advice concerning the movement of treated soils, have created new obstacles for those dealing with the plant. Although the code is not legally binding, it does set out best practice, and it is likely to be referenced in any civil or criminal action. Those who ignore its recommendations, therefore, do so at their peril.

Peter McKeon is a consultant ecologist at RPS Group and Emma Humphreys is an Associate at Charles Russell LLP

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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