Leeds’ research on Japanese knotweed to drive Parliament debate


There is no evidence that Japanese knotweed causes more significant structural damage to buildings than many other plants, a Parliamentary committee will hear today.

Research by ecologists from global infrastructure services firm AECOM and the University of Leeds is key evidence to be presented to the Science and Technology Select Committee of the House of Commons. It will be discussed in a session exploring the effects of Japanese knotweed on the built environment.

The select committee inquiry was formed following the publication of the AECOM and University of Leeds study that looked for evidence of Japanese knotweed’s perceived threat in previous research literature and assessed residential properties where the plant was identified.

The scientists, including Dr Karen Bacon from the School of Geography at Leeds, found no evidence to suggest that Japanese knotweed causes significant damage to buildings – even when it is growing in close proximity.

However, while it may not deserve its property damage stigma, it remains a threat to our native ecology. The negative impact it has on biodiversity and flood risk should not be ignored.

Dr Karen Bacon, School of Geography

Currently, when Japanese knotweed is identified in homebuyers’ surveys, mortgage lenders often require evidence that a treatment programme is in place to control Japanese knotweed, entailing significant expense for sellers. Property values can be affected, even after action is taken to control it.

Speaking ahead of today's select committee inquiry, Dr Bacon said: “Japanese knotweed poses less risk to buildings than many other common woody species, particularly trees.

“However, while it may not deserve its property damage stigma, it remains a threat to our native ecology. The negative impact it has on biodiversity and flood risk should not be ignored.”

The committee will hear from Professor Max Wade, Technical Director – Ecology at AECOM and study co-author, who will highlight the need for an updated and robust risk assessment on Japanese knotweed’s impact on structural damage as well the need to re-examine the current guidelines and policy on treating the plant when identified.

Before the inquiry, Professor Wade said: “This is a golden opportunity to put the impacts of Japanese knotweed into perspective, and by doing so save millions of pounds – in compensation for landowners and in property valuations for homeowners.”

Oral evidence will also be given by the Royal Institution of Chartered Surveyors, UK Finance, the Property Care Association and homeowners who have had Japanese knotweed identified on their property.

Read the full press release detailing the research findings, published in July 2018.

Further information:

Top image: Pixabay

‘Japanese knotweed (Fallopia japonica): An analysis of capacity to cause structural damage (compared to other plants) and typical rhizome extension’, by Mark Fennell, Max Wade and Karen Bacon, is published in PeerJ

For further details and interviews, contact Rachel Brierley at rachel.brierley@aecom.com or 07920 533 198; or Anna Harrison, University of Leeds Media Relations Manager via +44(0)113 343 4196 or pressoffice@leeds.ac.uk.

Further information for members of the public with concerns about invasive species and their property is available from the Property Care Association.