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Know your knotweed advice

By Nicola Temple

Researchers at the University of Exeter's Penryn campus have had a comprehensive look at Japanese knotweed (Fallopia japonica)  guidance from a range of sources on the web, including government sites, environmental NGOs, weed control companies, the media and the property market. They've found that this advice is often contradictory and even misleading.

A Japanese knotweed contaminated area in Hertfordshire
is identified with signage.
Photo credit: Peter O'Connor via Flickr [CC By-SA 2.0]
Japanese knotweed was introduced to the UK as an ornamental in the mid-1800s. It quickly became a problem plant, spreading swiftly and widely across the UK. This brutish invasive can penetrate building foundations and drains and is estimated to cost the UK economy £165 million a year.

The plant can grow from very small fragments of rhizome that weigh as little 0.01 g [1]. The rhizome material is capable of surviving for three months in a salty environment, which allows it to spread in coastal regions. Disturbing the rhizomes underground only promote growth and cutting the material above ground stimulates new above ground stems. It is the very definition of nuisance.

Japanese knotweed and the law

Two pieces of legislation were enacted to  provide the legal teeth needed to help control Japanese knotweed [2]. Under the Wildlife and Countryside Act 1981 (Section 14), it is illegal to plant or otherwise cause Japanese knotweed to grow in the wild. Offences can carry a maximum £5,000 fine or six months in prison, or both, in magistrates court. A Crown Court can impose an unlimited fine or maximum prison sentence of 2 years, or both.

The second piece of legislation is under the Environmental Protection Act 1990 (Section 33), where it is classed as 'controlled waste# and must therefore be disposed of according to the Environmental Protection Act (Duty of Care) Regulations 1991. If you keep, treat or dispose of knotweed in a manner that is likely to allow it to spread, a magistrates court can impose a maximum fine of £20,000 or prison sentence of 6 months, or both. A Crown Court can impose an unlimited fine or maximum prison sentence of 2 years, or both.

Allowing Japanese knotweed to spread to your neighbours can also be considered a private nuisance. Failure to control this plant on your land could therefore result in a prosecution or community protection notice.

Mixed messages
Japanese knotweed growing along a fence in East London.
Photo credit: Gordon Joly via Flickr [CC licence BY-SA 2.0]

The research, published today (4th July) in the journal Applied Ecology, included a content analysis, which objectively describes written, spoken and visual communication, and allows researchers to quantify different types of content. This is a method often used in social research, but rarely applied to ecological questions, such as invasive plants. The results showed that there is conflicting advice out there, particularly about the disposal of Japanese knotweed, which could result in people taking the wrong course of action that leads to the unlawful and environmentally harmful spread of the plant.

"It is important to provide clear advice about the waste disposal of Japanese knotweed," explained Beth Robinson, a PhD researcher in Exeter's Environment and Sustainability Institute and lead author of the study, "as it can regrow from small fragments of rhizome and incorrect disposal of waste material can result in further spread of this plant."

Even government websites were found to have conflicting and unclear information. The researchers point to Devon and Cornwall councils as both having valuable and accurate information about knotweed management. However, most of us are likely to consult the website of our own local council with the assumption that the information they provide is accurate.

"We recommend that local and national authorities collaborate and work towards disseminating more consistent messages," said Robinson.

A tendency by the media to sensationalise the risks associated with this invasive plant can lead to unnecessary anxiety and expenditure.  An extreme example of this was headlines in 2013 such as 'Murder andsuicide by husband driven mad over knotweed'. Stories such as this make it sound as though the plant might have a psychoactive effect - driving people mad by its sheer presence, when indeed there are serious underlying mental health issues.

The Exeter researchers stress that Japanese knotweed needs to be dealt with on a case by case basis. While some knotweed invasions do require professional assistance, small-scale occurrences in domestic gardens may be effectively controlled and disposed of responsibly by the homeowner.

Visit the Cornwall Council website for some reliable information about Japanese knotweed and its management. 


The paper in Applied Ecology is titled 'Weeds on the web: conflicting management advice about an invasive non-native plant' and is authored by Beth S. Robinson, Richard Inger, Sarah L. Crowley and Kevin J. Gaston.


Sources:

[1]     Macfarlane, J.S. (2011) Development of Strategies for the Control and Eradication of Japanese Knotweed [MPhil Thesis, University of Exeter] <https://ore.exeter.ac.uk/repository/handle/10871/11862>

[2]     Cornwall County Council (2016) 'Japanese Knotweed Legal Issues' [website accessed 4/7/2016] <https://www.cornwall.gov.uk/environment-and-planning/trees-hedges-and-woodland/invasive-plants/japanese-knotweed/japanese-knotweed-legal-issues/>

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