Japanese Knotweed is an invasive, non-native species (sometimes referred to as “alien species”). As its name suggests, it is native to Japan, where the plant is known as “itador”: one interpretation of this name is that it comes from a word for  “remove pain” which alludes to its painkilling and medicinal use. It is used to treat a variety of ailments, including cardiovascular diseases, skin inflammation and fungal infections.  The Royal Botanic Gardens Edinburgh received plants named Polygonum seiboldii in 1854 and commercial sales of knotweed took place in Britain after then.  It was sold as an ornamental fodder plant with the ability to stabilise sand dunes because of its vigorous growth habit and its ability to form dense screens.  It was also used as an ornamental plant.  It is now the most invasive plant in the UK.   This perennial spreads rapidly by its roots (rhizomes) and stems and is extremely difficult to eradicate.  Between April and October, it can grow up to 10 centimetres a day.  Even if a small piece of the plant is left in the ground, it can regenerate and the roots can extend to 7 metres laterally and 3 metres in depth.  It causes substantial damage by penetrating foundations, walls, drives and paths and is very expensive to remove.  The government has estimated the cost of eradicating it from all the UK at £2.6 billion. 

In the UK, there appears to have developed a hybrid, Bohemian Knotweed (a cross between giant Knotweed and Japanese Knotweed), which may prove more destructive than its parent plant. 

The eradication of Japanese Knotweed requires treatment with herbicide (which may only make it dormant) or excavation (which may fail if any fragments remain in the soil.).

The Japanese Knotweed Alliance provides practical information on knotweed control – cabi.org/japaneseknotweedalliance/.  A biological control using insect, a psyllid called Aphalara itadori, are being trialled. 

Schedule 9 to the Wildlife and Countryside Act 1981 (“WCA 1981”) lists certain non-native species, including knotweed (“Fallopia japonica”), that have become established in the wild in Great Britain, but which the law seeks to prevent spreading further (unless a licence is obtained).

Someone is guilty of an offence if they plant knotweed or otherwise cause it to grow in the wild.  It is also an offence to sell, offer or have or transport knotweed for the purposes of sale.

It is a defence to prove that all reasonable steps were taken and all due diligence was exercised, provided that 7 days’ notice is given to the prosecution that such a defence is to be relied on.

Penalties include up to 2 years’ imprisonment and/or an unlimited fine.

Guidance issued by Defra explains that Defra would expect the landowner or occupier to take reasonable measures to confine knotweed to the cultivated areas so as to prevent it spreading to the wider environment and beyond the landowner or occupier’s control. Failure to take reasonable measures to confine knotweed to the cultivated area that results it spreading into the wild could be considered as “causing to grow in the wild” and, consequently, an offence.  If someone introducing knotweed into a private setting does not have sufficient ability or resources to manage it so as to prevent it spreading to the wild, they should seriously consider whether planting it is appropriate.  Negligence or reckless behaviour (such as inappropriate disposal of garden waste) that results in knotweed becoming established in the wild would constitute an offence, so beware taking it to your local council dump or recycling facility.

A company officer, as well as a company, can be guilty of the offence and liable where the offence is proven to have been committed with their consent or connivance, or is attributable to their neglect.  The same applies to partners and partnerships.

An offence will void a permit or licence and the court can order an offender not to be issued with any permit or licence for up to five years.  

A due diligence offence may be available is someone can demonstrate that they took all reasonable steps and exercised all due diligence to avoid committing the offence.

An enforcement officer can enter premises without a warrant, on strict justification, where there are grounds of suspicion that a specimen is being kept on those premises.  Entry to private dwellings is only permitted with a warrant from a justice of the peace.  There are powers to seize specimens at UK borders.

There are also similar sanctions available for minor breaches including fixed and variable money penalties where a custodial sentence is inappropriate, compliance, restoration and stop notices, enforcement and third party undertakings.

It is an offence to introduce knotweed from ships, but a defence to prove that the introduction resulted from the discharge of water carried as ballast, that the discharge was necessary for safety purposes and all reasonably practicable steps were taken to avoid the introduction  occurring, or the risk of it occurring, in an area where it could risk harming natural habitats.

Environmental authorities have powers to enter into a voluntary Species Control Agreement (SCA) with an owner of premises and, if necessary, to impose a Species Control Order (SCO) on the owner.  These can provide for either the owner or the authority to carry out the control operations.  Compensation may be available for owners suffering financial loss resulting from an SCA or SCO or from powers of entry being exercised.

When Japanese Knotweed is disposed of as part of the removal process, it is likely to be classified as controlled waste. This will usually be as part of topsoil removal and ground works for development.  Untreated Japanese Knotweed will not usually be classified as (far more serious) hazardous waste until sprayed with harmful herbicides. Knotweed sprayed with herbicide but left in the ground will not be classified as controlled waste (or hazardous waste).  It is not lawful to dispose of Japanese Knotweed with other surplus soil or sell soil contaminated with Japanese Knotweed as topsoil.  

As a result of being controlled waste, the following waste offences may be relevant:

• Depositing control waste (or knowingly causing or knowingly permitting it to be deposited) in or on a land without a permit, or in a manner likely to cause pollution to the environment (section 33 Environmental Protection Act 1990) (“EPA”);
• Breaching a duty of care by failing to take all reasonable steps to ensure that the waste is not disposed of unlawfully or in a way that causes pollution or harm (section 34 EPA 1990);
• In addition, the controlled waste must be transferred to a registered carrier (or exempted carrier) and a Waste Transfer Note (WTN) must be completed and signed, giving a written description of the waste.

Defence to section 33 include taking all reasonable precautions and exercising all due diligence to avoid the commission of the offence and acting in an emergency.

The offences may incur a term of imprisonment of up to 5 years, an unlimited fine or both.

A local authority can serve a notice on an occupier of land requiring it to remedy the condition of land within a specific period where, in the local authority’s opinion, the immediate area, or adjoining area, is adversely affected (section 215 Town & Country Planning Act 1990 (“TCPA 1990”).  This power could be exercised for infestation of any land by knotweed, particularly where it is at risk of spreading into adjoining land.  A minimum of 28 days’ notice to remedy must be given, during which the occupier can appeal all grounds including that infestation does not adversely affect amenity, that the condition of the land results in the ordinary course of events, requirements of the notice are excessive or time for compliance is unreasonable.  Failure to comply with the notice may lead to prosecution, a fine of up to £1,000 and the local authority stepping in to undertake the necessary work and recover its costs from the occupier.

There is also a possibility that the police might serve a community protection notice if the knotweed 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 of an individual body in that respect was unreasonable.  This conduct might include a failure to act.  The community protection notice can place restrictions on someone’s behaviour and force them to control knotweed. Failure to comply with the notice might lead to a fine of up to £2,500 and, again, the local authority can step in to resolve the problem. 

There is no general duty to control, remove or report knotweed.  However, it is prudent land management to take action promptly to control the spread of the plant and to avoid the consequences set out above. Nor is the owner or occupier of the land obliged to report knotweed to the authorities. 

If an owner or occupier allows knotweed to spread on to neighbouring land, they may find themselves a defendant in private nuisance proceedings by their neighbours for the loss of enjoyment or amenity (which might amount to diminution in value of the property), the costs of removal and an injunction against reinfestation and/or requiring action to control the knotweed.

The presence of knotweed can affect adversely the value, marketability and insurability of land and buildings.  Whilst there is no blanket policy for lenders which prevents them from lending on properties which have knotweed, the difficulty in treating it has led to some historical reluctance to lend.

Buildings insurance policies generally do not cover damage caused by knotweed.  Where work is done to eradicate knotweed, it is worth considering whether to use a specialist company that provides a guarantee of ongoing treatment cover if the knotweed regrows or if the original work was faulty.  This guarantee maybe backed by insurance, so might offer protection if the original company has ceased to trade. Many of these products have been designed to meet the demands of insurance companies, banks and building societies.

The principle of caveat emptor (“buyer beware”) means that (subject to some exceptions), where the property is sold or let, the seller or landlord is not under a duty to disclose any information about the physical condition of the property. The buyer or tenant will usually raise pre-contract enquiries to establish more information.

However, the standard pre-contract enquiries for commercial property asks for details of infestation, hazardous substances or contaminative (or potentially contaminative) material or environmental problems.  Arguably, these enquiries may apply to knotweed. 

The rural and agricultural land standard pre-contract enquiries specifically ask whether the seller is aware of Japanese Knotweed.

Residential property pre-contract enquiries ask whether the property is affected by Japanese Knotweed, whether there is a management and treatment plan or insurance cover.  

Leases may cover the responsibility of either landlord or the tenant for dealing with knotweed.

The Land Remediation Relief (“LRR”) scheme was extended to include expenditure incurred in removing knotweed from land in a contaminated state, including contamination by knotweed after the land was acquired by the company claiming LRR, if it did not plant the knotweed or allow it to spread.  For example, LRR is available for removing knotweed introduced by fly tippers.  LRR is not available for disposal of knotweed to landfill.  However, it is available for other methods, including off-site treatment.

It is common and good practice in most property transactions to commission an environmental desktop report from an environmental consultancy.  However, those types of reports are based on publicly available information and do not include a site visit, so would not usually reveal whether knotweed is present on the property.

Therefore, if a buyer is concerned about knotweed (for example, because they plan to redevelop the site) they should commission a specific knotweed survey and assessment.