Japanese knotweed (Fallopia japonica) is one of the most invasive plant species in Britain. It is a hardy, bamboo-like perennial plant that, although quite attractive on first glance, is highly aggressive and destructive. It has been known to block footpaths, grow through concrete, damage tarmac, flood defences and homes1.
Japanese knotweed was originally introduced by botanists in the mid nineteenth century and has now spread to such an extent that it is present in almost every 10km × 10km grid square in the country. It grows as much as 20 centimetres per day in any type of soil, and can reach a height of up to 3 metres in a few months1. Even though it does not produce viable seeds in the UK, its spread is almost unstoppable as it grows through rhizomes fragments (underground root-like stems that can be as small as a few millimetres) meaning individual plants can cover several square metres via an extensive underground rhizome network. This makes it extremely difficult to fully remove once established.
It was recently reported that the use of psyllids (plant feeding insects that will feed on Japanese knotweed) is being trialled in field tests. It is hoped that this will help control the spread of the plant4, though complete eradication requires closely monitored herbicide treatment at specific times within the plant’s life cycle.
Treating an infestation of just a few small square metres can cost upwards from £5,000, especially if a quick solution or complete rhizome excavation is required. Larger infestations, and particularly those that require offsite disposal of significant volumes of controlled waste, are likely to cost tens to hundreds of thousands of pounds to be effectively dealt with2.
Given its virulence and the cost of eradication, it’s not hard to see why Japanese knotweed has become a major issue in property transactions. In the last few years lenders have become particularly aware and sensitive to the issue and many have formalised their secured lending decisions concerning property affected by knotweed infestations. On occasion, this has resulted in mortgage refusals as the risk has been deemed too high. Back in 2012 The Guardian reported the story of Mr Gingell, whose house sale fell through two weeks before the exchange date due to the presence of a 3cm high Japanese knotweed plant found in his back garden3. For these reasons it is important to be informed ‘as much as possible about whether it’s a problem in a property you’re looking at’4.
In an attempt to counteract the rising concerns over Japanese knotweed and its effects, the RICS (Royal Institution of Chartered Surveyors) guidance paper, completed with the support of the Property Care Association (PCA) Invasive Weeds Control Group, was published in March 2012. This has generally led to an accepted situation where lending will likely be agreed where a suitably robust Japanese knotweed remediation programme is established, and a ten year insurance backed guarantee is in place. Despite this, it is widely reported that lenders are still seeking a 15% to 20% diminution in property value where such remediation schemes are in progress2.
So what is your responsibility as a landowner if you find Japanese knotweed on your property? It is not yet an offence to have Japanese knotweed on your land and there is no legal obligation to remove it or notify anybody. However, allowing Japanese knotweed to spread onto your neighbour’s property/land may constitute a private nuisance under common law, potentially resulting in an injunction requiring you to abate the nuisance3.
Recently, the Law Commission review of wildlife law in England and Wales concluded that the existing legislation is not sufficient to control and eradicate invasive non-native species. The Infrastructure Bill will amend the Wildlife & Countryside Act 1981. A new Schedule 9A will be inserted into the Act to empower environment authorities to enter into “species control agreements” (SCA) with owners of premises where the authority considers that an invasive non-native species is present. Further powers will be given to the environment authorities to make species control orders (SCO). If the owner of premises has failed to comply with or agree to an SCA, the authority can make an SCO. This can require the owner to carry out species control operations or can allow the authority itself to do so.
Very recent legislative changes have also seen the issues surrounding Japanese knotweed enter into the Anti-social Behaviour, Crime and Policing Act 2014. The new rules state that people and organisations who fail to control Japanese knotweed could be issued with anti-social behaviour orders (Asbos) if their conduct is having ‘a detrimental effect of a persistent or continuing nature on the quality of life of those in the locality, and that the conduct is unreasonable’6. Conviction under the Act would be a criminal offence and individuals could be fined up to £2,500, with companies facing fines of up to £20,0005.
So, while the removal, eradication and disposal of Japanese knotweed can be expensive, given the potential costs associated with legal action, repairs and diminished property value, the most cost-effective approach is often appropriate removal and disposal by licensed contractors.
If you are interested in learning more about the identification, reporting and/or remediation of this invasive plant please download a copy of GroundSure’s definitive guide to Japanese knotweed.
References
1https://www.gov.uk/japanese-knotweed-giant-hogweed-and-other-invasive-plants
2GroundSure Japanese knotweed Guide
3http://www.theguardian.com/money/2012/sep/08/japanese-knotweed-house-sale
