What is it?
Japanese knotweed is a large perennial plant native to East Asia in Japan, China and Korea. It has hollow stems that give it the appearance of bamboo. In some parts of Japan it has been cultivated for food (it has a flavour similar to extremely sour rhubarb) and it is used in traditional Chinese medicine.
In the West, Japanese knotweed was once popular but has now been listed by the World Conservation Union as one of the world's worst invasive species and described by the Environment Agency as "indisputably the UK's most aggressive and destructive plant".
Why is it a problem?
The invasive root system and strong growth can damage concrete foundations, buildings, road, paving and flood defence and is expensive to remove. According to research conducted by the BBC, Japanese knotweed costs the UK economy around £165 million every year.
What if it is on my property?
Concerted efforts should be made to remove Japanese knotweed from any property. Although DIY treatments are available, it is complicated and time consuming to treat, so it is much better to bring in professionals who will carry out a site survey and prepare a treatment and removal programme.
Bear in mind that many banks will refuse to lend on a property if Japanese knotweed is found to be present. It can also cause delays and increased costs to development works. If knotweed encroaches onto adjoining land, this can lead to a damages claim for private nuisance.
What if it is on adjoining property?
Banks may still refuse to lend if Japanese knotweed is found on an adjoining property. In the recent case of Williams v Network Rail (February 2017, County Court), a Mr Williams and Mr Waistell sued Network Rail because Japanese knotweed on a nearby rail embankment had devalued their homes, after lenders refused to accept the property as security.
The knotweed had not yet spread to the claimants' properties or caused any physical damage to them. Nevertheless, the court ruled that the presence of knotweed on the adjoining embankment was an actionable nuisance.
The judge said a property's value is not simply the use and enjoyment of it, but can also include the ability to sell it at a proper value. Finding that Network Rail had failed to take reasonable steps to minimise risk to its neighbours' land, he ordered payment of remediation costs plus compensation for any residual fall in the property' value.
The decision is not binding on high court judges but it would seem to extend the law by making a landowner liable even if the knotweed has not yet spread to adjoining land because it is a "Proximate Nuisance".
What is the significance of this decision?
Landowners need to take appropriate steps to control/eradicate Japanese knotweed from their properties. This can prove very costly for individuals, local authorities and other large landowners.