UK: Alien Invasion: Japanese Knotweed

Last Updated: 17 July 2018
Article by Verity Gawthorp

This article considers the risks of allowing japanese knotweed to spread on your land and the steps which a landowner can take.

Japanese knotweed is, let's face it, a rather boring looking plant and most people would admit to not being able to recognise it if it was growing on their property.  However, this innocuous-looking plant can, if not dealt with properly, have a devastating impact on the value of land.  Here we consider the risks of allowing japanese knotweed to spread on your land; the steps which a landowner can take if japanese knotweed is threatening to invade your land from a neighbouring property; and what you should do if you suspect that japanese knotweed may be growing on your land.

Japanese Knotweed: Why is it such a problem?

Japanese knotweed (also known as, amongst other things, german sausage plant, hancock's curse and donkey rhubarb) was introduced into the UK in the 19th century as an ornamental garden plant.  However, in the absence of its usual competitors, diseases and the animals which like to eat it, it quickly began its uncontrolled spread across the UK and is now considered to be a serious threat to land.

The first question that most people will ask is what does japanese knotweed actually look like?  It is easy to confuse japanese knotweed with various other species, such as dogwood and Himalayan balsam.  However, japanese knotweed grows rapidly in summer producing stands of canes which resemble bamboo (although it is not related to bamboo), with leaves which are heart- or shovel-shaped and up to 14cm in length, along with creamy coloured flowers which appear in late summer and early autumn.  The plants die back to the ground in winter – however the dry canes can remain in situ for longer.

Japanese knotweed causes problems through its ability to spread rapidly by means of its root system and its stems.  Its roots (also known as rhizomes) can extend down into the soil to a depth of around three metres and can spread horizontally through the soil for up to approximately seven metres.  It is also capable of growing up to ten centimetres a day at certain times of the year.  This has made japanese knotweed one of the most invasive species in the UK and very hard to eradicate in its entirety.  Even if one small section of the plant is left in the soil, japanese knotweed is capable of regenerating and re-establishing itself.

Japanese knotweed also causes problems through the ability of its roots to grow through the foundations of buildings, as well as concrete and walls – thus potentially causing significant damage.  Japanese knotweed can be a very expensive plant to remove completely.  In order to eradicate the plant, either all of the above-ground sections of the infestation must be treated with herbicides repeatedly for several years or, alternatively, the entire root system must be dug out of the ground and disposed of safely.  Both systems of eradication can be costly procedure and could total hundreds of thousands of pounds if the infestation is particularly large and the entire root system needs to be removed.

The presence of japanese knotweed on land (or even neighbouring land) can have a serious and detrimental effect on the value, marketability and insurability of the land concerned.

The Council of Mortgage Lenders (now integrated into a new trade association, UK Finance), state that the presence of japanese knotweed should be mentioned on a residential valuation report.  Some lenders have their own individual policies as regards lending on properties affected by japanese knotweed, although many are reluctant to do so.  If a lender is willing to lend on property affected by japanese knotweed, it is likely to insist on a programme of eradication being put in place as a condition of its lending, with the works covered by a ten-year insurance backed guarantee.

All in all then, the possible presence of japanese knotweed is a serious concern for landowners.

What are the risks if you have japanese knotweed on your land?

The first point to note is that there is no legal obligation on a landowner to remove japanese knotweed from land, or report its presence to the authorities.  However, it is highly unlikely that, if you have japanese knotweed on your land, you will be able to contain it in such a way so as to prevent its growth into other areas.  The spread of japanese knotweed can potentially leave a landowner facing both criminal and civil liability. As regards criminal liability, there are various pieces of legislation which can impose criminal sanctions on a landowner in relation to the presence of japanese knotweed on their land.  These include:

  1. The Wildlife and Countryside Act 1981 – under which a landowner, who plants or knowingly allows japanese knotweed to grow on his land and thereby cause problems as it spreads to other areas of the wild and who make a conscious decision to do nothing about it, could be guilty of a criminal offence and liable on conviction to imprisonment and/or a fine;
  2. The Infrastructure Act – under which certain environmental authorities have the power to enter into Species Control Agreements ("SCA") with landowners to assist in the control of japanese knotweed.  If the landowner fails to comply with the terms of the SCA, or if the matter is an urgent one, the environmental authority can make a Species Control Order ("SCO"), compelling the landowner to carry out the control operations required.  If a landowner is found to be guilty of failing to comply with an SCO, they could be liable to imprisonment and/or a fine;
  3. The Town and Country Planning Act 1990 – under which a local authority has the power to serve a notice on the occupier of land infested with japanese knotweed, requiring them to remove it if the local authority believe that the amenity of an area, or the land adjoining it, is adversely affected by the presence of japanese knotweed.  Failure to comply can lead the occupier, on conviction, to be liable to pay a fine;
  4. The Anti-Social Behaviour, Crime and Policing Act 2014 – under which a local authority, or the police, are able to serve a community protection notice on an individual or an organisation due to the fact that japanese knotweed is not being controlled on the land concerned, when the party concerned could reasonably be expected to do so and this is having a negative effect on the quality of life of local people.  Failure to comply with the notice is a criminal offence and, as above, can lead to a fine; and
  5. The Environmental Protection Act 1990 – when japanese knotweed is removed from land, the soil and plant matter removed will be classed as controlled waste.  Under this Act, it is an offence to deposit controlled waste on land without a permit, or in a way which is likely to cause pollution of the environment.  The waste must also be carried by a registered carrier along with a waste transfer note.  If a person is found guilty of breaching these provisions, they can be liable, on conviction, to imprisonment and/or a fine.

As well as the various offences a landowner could face under criminal law, detailed above, a landowner could also be subject to a common law claim by a third party if japanese knotweed on the land concerned has caused damage to, or loss of enjoyment of, the third party's property. 

What can you do if your land is affected by japanese knotweed?

If there is japanese knotweed on neighbouring land and this is being allowed to grow and spread on to your property, you may be able to successfully bring a claim in common law for private nuisance.   There have also been a couple of recent cases which have highlighted this issue (the joined cases of Waistell v Network Rail Infrastructure Limited and Williams v Network rail Infrastructure Limited – referred jointly as Waistell v Network Rail; and Smith & another v Line).

Each case involved the presence of japanese knotweed on the defendant's neighbouring land.  The claimants argued that the presence of the japanese knotweed had caused a diminution in the value of their properties due to nuisance on the basis of:

  1. Physical encroachment on to the claimants' land (trespass); and
  2. Interference with the amenity of the claimants' land (that is, their enjoyment of their land) as a result of the presence of japanese knotweed on the defendants' neighbouring property

Each of the cases was heard in the Crown Court, where it was held that:

1. The mere presence of japanese knotweed on the claimants' land would not constitute and actionable nuisance unless the japanese knotweed had caused some physical damage to the land concerned.

2. The presence of japanese knotweed on neighbouring land in close enough proximity to the border with the claimants' land will, however, have a negative effect on the value of the claimants' land and would therefore be an actionable nuisance on amenity grounds.

Network Rail appealed the decision of the County Court in Waistell v Network Rail and the Court of Appeal have recently published their decision.  The Court of Appeal have upheld the County Court's decision but for different reasons. 

The Court of Appeal have held that the presence of japanese knotweed not only carries the risk of future physical damage to buildings and other structures on the land concerned, its presence creates and increased difficulty in the ability and cost of developing the land.  The Court of Appeal held that japanese knotweed can therefore be defined as a "natural hazard".  Its presence affects a landowner's ability to fully enjoy their land and consequently interferes with the land's amenity value.  The Court of Appeal saw no reason why, in appropriate circumstances, a claimant should not be able to obtain an injunction where the amenity value of the land has been reduced by the presence of japanese knotweed on the land itself, even if there has been no physical damage.

What, therefore, can a landowner do who suspects that there may be japanese knotweed on, or in close proximity to, his or her land?

If you are concerned about the potential presence of japanese knotweed, it would be advisable to consider obtaining a specialist japanese knotweed search report (this could be a desktop survey or a full site inspection) for the land you are concerned about.  If there is japanese knotweed present on your land, specialist invasive weed professionals can be instructed to advise on the steps which need to be taken and the likely costs.  Even if a landowner has no immediate intentions to sell, lease, develop or mortgage the land in question, it is always worth considering whether taking steps now to eradicate the problem (when the landowner has several years in which to undertake the work involved) will be a more cost effective way of controlling the infestation than the actions which may be required if the japanese knotweed needs to be removed as a matter of urgency.

And, if all else fails, you could always cook it and eat it.  Japanese knotweed tastes like rhubarb apparently...

The content of this article is intended to provide a general guide to the subject matter. Specialist advice should be sought about your specific circumstances.

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