Japanese knotweed is an innocuous looking non-native herbaceous plant that reproduces through its root system or via the dispersal of fragments of its fleshy, hollow stems. It’s ability to quickly colonise fresh ground is notorious. As a result, it’s often found growing in Irish gardens and parks (especially old ones), as well as on waste-ground, rubbish tips or roadsides, usually transported there Trojan-horse style via contaminated soil. For this reason it has become one of Europe’s most hated weeds and its extensive root system is capable of undermining building foundations, roads and walls.
Under the EU Regulation 1143 2014 on the control of invasive alien species , local authorities and property owners have an obligation to take proper measures to control/ eradicate the plant.
Under Regulation 49(2), any person who plants, disperses, allows or causes to disperse, spreads or otherwise causes to grow Japanese knotweed or any of the other invasive plants listed in the Third Schedule of the European Communities (Birds and Natural Habitats) Regulations, 2011 (S.I. No. 477 of 2011) shall be guilty of an offence.
Furthermore, Sections 52(7) and (8) of the Wildlife Act, 1976, as amended, make it an offence to plant or otherwise cause to grow in a wild state exotic species of plants.
If you have concerns about the existence of the plant, then you should take immediate steps to firstly, correctly identity the plant and secondly, take appropriate advice on the safe and legal means or treating and removing the plant. You are legally required to obtain a licence from the National Parks and Wildlife Services for the safe disposal of Japanese knotweed plant material or of contaminated soil.
Property owners should beware of their responsibility to prevent the spreading of the plant. Failure to prevent the spread of the plant may result in an adjoining property owner bringing a tortious action, under private nuisance.
To date there have been no reported cases of Japanese knotweed actions in Ireland. However, the recent UK case of Williams & Waistell v Network Rail is instructive. In this case a Cardiff Court found Network Rail responsible for an actionable nuisance for failing to take steps to prevent Japanese knotweed from affecting properties close to its railway embankment. Network Rail appealed and the Court of Appeal handed down judgment in July 2018 and found against Network Rail, albeit on different reasons than the Court of first instance (Network Rail Infrastructure Limited v Williams & Waistell  Civ 1514).
In brief the Court of first instance found that even though there was no physical damage and no effect on the utility of the land of Williams and Waistell, that the amenity value of a property is not simply the use and enjoyment of the land, but can include the ability to dispose of it at a proper value. The Court rejected this as being equivalent to pure economic loss and held that that the presence of the Japanese knotweed had devalued the claimants’ property and even if treatment took place, their saleable values would still be below the market value.
In contrast the Court of Appeal held that the Court of first instance was wrong in so far as it effectively extended the tort of nuisance to a claim for pure economic loss. The Court of Appeal clarified that the purpose of the tort of nuisance is not to protect the value of property as a financial asset but to protect the landowner in their use and enjoyment of the land.
However, the Court of Appeal did not agree with the Court of first instance’s dismissal of the original physical encroachment claim, which was based on the spread of the Japanese knotweed’s rhizomes onto the claimants’ land. The Court of Appeal held that the mere presence of Japanese knotweed and its rhizomes constitutes “a natural hazard which affects landowners’ ability fully to use and enjoy their property and, in doing so, interferes with the land’s amenity value.”
Thus the Court of Appeal affirmed that the mere presence of Japanese knotweed constitutes damage of a sort that will ground a claim in nuisance. The court noted the findings at first instance as to Network Rail’s actual and constructive knowledge of the presence of the knotweed and the potential risks arising to adjoining properties. It also accepted that Network Rail had failed reasonably to prevent the interference with the claimants’ enjoyment of their properties.
Potential effect on property valuations
In the UK the Council of Mortgage Lenders’ policy states that the presence of Japanese knotweed might affect the valuation of a property. Valuers who inspect property for mortgage purposes are generally instructed to report to lenders where knotweed is present and action is usually required if the plant is found within 23ft of a structure.
While Irish valuers are not yet obliged to disclose Japanese knotweed on property valuation reports, it can only be a matter of time as the spread of knotweed is endemic throughout the country.
As Japanese knotweed grows in rural and urban areas it is incumbent on all property owners or buyers of residential, commercial or agricultural property, to check for new or unfamiliar plant growth. Failure to do so could have hidden and costly repercussions.