Written evidence submitted by
Sean Hathaway, Environment Officer, Swansea Council (JKW0003)
Submission to the queries outlined below;
• What scientific evidence exists on the effects of Japanese Knotweed on the built environment?
Several papers and relevant policies documents cite property damage caused by knotweed eg;
Environment Agency Code of Practice 2013;
Property Care Association Code of Practice 20/3/13; ‘In Practice’ bulletin of Institute of Ecology and Environmental Management, no. 72, June 2011, (ISSN 1754-4882), chapters-Invasive Weeds:
A Barrier to Development, Environmental Catastrophe or Manageable Nuisance? Thurlow Countryside Management (TCM) and
The Myths of Japanese Knotweed A Critical Appraisal/Review of the UK Knotweed Industry by Maxime Jay Musketeers Group Ltd.
The commonly mentioned maximum 7m extension of underground rhizome spread is from an older scientific paper (probably by Beerling, D.J., Bailey, J.P. and Conolly, A.P or Child L.E) but seems to have been taken as the usual distance used when surveying properties for knotweed. In practice the distance is much smaller.
The PCA White Paper White Paper Advice for Developers Jan 14 mentions the 7m rule.
• How the presence of Japanese Knotweed in the UK affects mortgage lending decisions and property valuations;
The presence of knotweed has been used as a reason to de-value properties or in some cases to make them un-marketable which obviously causes a lot of unnecessary stress, delays and costs to both the buyer and seller. In addition other plants are mis-identified as knotweed including horsetail, buddleia, bindweed, Acanthus mollis, periwinkle, tutsan/St John’s Wort, pheasant berry and Himalayan balsam.
In one local case a surveyor included knotweed as being present by the property and according to the seller the reason they used was “I can’t see it but it’s got to be here somewhere”
The mortgage TA6 form includes questions about knotweed.
• Whether mortgage lending decisions relating to the presence of Japanese Knotweed are currently based on sound scientific evidence of its effects on the built environment;
As far as I’m aware there is little scientific evidence of structural damage caused by knotweed. Other species such as bamboo and buddleia cause more problems as do tree roots. Dr Karen Bacon from the University of Leeds School of Geography has carried out research suggesting that there is little evidence supporting the fact that knotweed causes damage. Most of the established knotweed control companies agree that damage is over exaggerated. The only knotweed stories in the press are scare stories, mostly of houses not being marketable due to knotweed as opposed to being physically damaged.
• What guidance for the sector currently exists, the impact of existing legislation, and how else evidence-based responses to the presence of Japanese Knotweed can be encouraged?
Guidance includes;
Royal Institute of Chartered Surveyors (RICS) Japanese knotweed information paper 1st Edition (27/2012) includes the knotweed risk category (enclosed). This paper needs to be updated to reduce the distances where knotweed is by a property or boundary to make property sales easier.
Property Care Association (PCA) Code of Practice 2018
Invasive Non Native Species Association Code of Practice Apr 2017
Council of Mortgage Lenders Japanese knotweed and other invasive plants
Gov.UK Prevent Japanese knotweed from spreading
The Property Codes Compliance Board, Search Industry Code of Practice and the Invasives Code
In conclusion;
The problem caused by knotweed in relation to mortgages is not a physical problem caused by the plant but a perceived problem by the lenders caused by mis information and fear.
Swansea Council and knotweed
Swansea Council has been involved with knotweed for over two decades and this list is a brief overview of involvement to date.
1992 Urban knotweed survey
1993 Conference
1994 First large scale treatment programme
1995 Knotweed planning condition introduced (approx 50/pa)
1997 Swansea Council Knotweed Action Plan
1998 Urban survey (measure increase from 1992)
1998 County wide survey (100 hectares)
1998 Knotweed officer appointed (initially a 3 year post). Me but still dealing with INNS now.
2000 The Knotweed Manual launched
2001 “No knotweed” warning on garden waste bags
2002 100 years of Knotweed in Glamorgan conference
2005-8 Last large scale treatment programme, approx 100,000m2
2011 Wales Natural control trials (knotweed)
2012 INNS flora planning condition introduced
2015 Wales Natural control trials (balsam)
1/8/15 Parks dept’ launch payable knotweed control service
These two papers IUCN IAS 2013 Japanese knotweed (Fallopia japonica) in Swansea in the City and County of Swansea – a local authority perspective and Aspects of Applied Biology, Surveys on the spread of Japanese knotweed Fallopia japonica in Swansea and strategies for its control (2000) discuss the role of Swansea Council.
The CABI report of the Economic Cost of INNS to Great Britain 2010 also mentions Swansea’s knotweed.
I hope this helps with the inquiry and please let me know if you need any further information.
December 2018