Japanese knotweed (Fallopia japonica) is native to Japan, Taiwan and northern China, and was introduced to the UK in the early 19th century as an ornamental plant. It is a perennial plant, growing each year from its extensive underground rhizomes, and spreads rapidly both by natural means and as a result of human activity.
Japanese knotweed is spread by fragments of rhizome or stem being transported to new sites. Very small fragments of stem/rhizome can give rise to new plants. The plant forms dense stands, outcompeting our native vegetation and causing nuisance and structural damage.
The responsibility for controlling Japanese knotweed always lies with the landowner.
This is the case for all sites including river banks. Natural Resources Wales do not own rivers or river banks (unless they are within our landholdings or on land for which we are responsible eg NRW nature reserves and Welsh Government Woodland Estate).
We carry out treatment of invasive species on our own land and on our flood risk management assets, but we are not responsible for treating invasive species on rivers and banks owned by other parties.
If you are unable to find out who owns the land in question, you may be able to find the information by carrying out a land registry search.
This content is for information only. If you have legal concerns about Japanese knotweed we recommend that you take specific legal advice.
It is not an offence for a landowner to have Japanese knotweed growing on their land and they don’t have to report its presence.
However, if Japanese knotweed is causing a nuisance there may be a civil liability.
Waste material from these plants is classed as ‘controlled waste’ under the Environmental Protection Act 1990 and must be disposed of at a suitably licensed or permitted waste site. Certain herbicides and plant material containing herbicides may also be considered as hazardous waste under the Hazardous Waste Regulations. If using a carrier to move this waste off site you must ensure they are a registered waste carrier.
Wildlife and Countryside Act 1981
Japanese knotweed is listed in Schedule 9 of the Wildlife and Countryside Act 1981 and is subject to Section 14 of this Act. It is an offence to plant or cause this species to grow in the wild. This means that actions which cause the spread of Japanese knotweed, eg strimming, flailing or dumping contaminated material, may constitute an offence. Allowing Japanese knotweed to spread from your property into neighbouring land may also be an offence, although this has not yet been tested in the courts.
Japanese knotweed offences under this Act are enforced by the police and local authority. Therefore, if you see somebody causing the spread of Japanese knotweed, you should contact your local police station.
If you need more information on section 14 refer to the guidance produced by DEFRA and Welsh Government.
Anti-social Behaviour, Crime and Policing Act 2014
Community Protection Notices can be issued by local councils or the police under the Anti-social Behaviour Crime and Policing Act 2014. These notices can be issued to individuals or organisations to compel them to control invasive species in situations where they are having a detrimental effect on the quality of life of others.
NRW does not issue these notices. Contact your local authority or the police if you require more information. Further guidance can also be found on the Home Office website.
Treatment and control of Japanese knotweed
DO NOT strim, flail or mow Japanese knotweed.
Doing so is likely to significantly increase the risk of spreading the plant and could constitute an offence.
Cutting and digging are NOT effective methods for controlling established Japanese knotweed and take many years to have any effect. Japanese knotweed has an extensive underground rhizome system which can be up to several metres deep, making it extremely difficult to dig up all rhizomes. It is highly likely that rhizomes will remain in the ground and give rise to new plants. These options also create controlled waste which must be carefully contained and disposed of in a specific manner.
Japanese knotweed is best controlled by the application of a suitable herbicide.
Glyphosate-based herbicides are commonly used to treat Japanese knotweed. If glyphosate is applied correctly, at the appropriate time of year, it is possible to eradicate it, although it can take two to three years of repeated treatment.
Professional glyphosate products are required as the type of glyphosate product bought at garden centres will have limited effect. Professional herbicide products must only be used by suitably qualified individuals who hold the necessary National Proficiency Test Council certificates of competence. Suitably qualified operators may be found locally or via an industry body.
To achieve control of Japanese knotweed, glyphosate must be applied in late summer/autumn after the plant has flowered. Applying glyphosate earlier in the year may stunt growth, but it will not kill the plant. Large mature stands of Japanese knotweed will need to be treated for two or three years to achieve eradication (ie treat once a year in late summer/autumn).
If you wish to use herbicides in a location that is in water, within a protected site, or near a water abstraction, you will need prior written approval from NRW.
Please read more information on applying for approval to use herbicides.
Advice for Contractors and Developers on disposal of contaminated material
Managing Japanese knotweed on a development site may require burning, burial or disposal of Japanese knotweed-contaminated material. Such activities should follow the Japanese knotweed Code of Practice to avoid committing an offence.
Japanese knotweed (or contaminated material) is a controlled waste, and as such must be disposed of at a suitably licensed or permitted landfill.
Welsh Government have advice on model specifications and guide to procurement for the control of Japanese knotweed in construction and landscape contracts.
For further information on the identification, control and disposal of Japanese knotweed, and the regulation of pesticides, see the following links:
- Welsh Government advice on invasive non-native plant species
- UK government advice on Japanese knotweed
- including a Horticultural Code of Practice which is also aimed at gardeners
- The GB Non-Native Species Secretariat website is useful for species information and tells you how you can record the presence of Japanese knotweed
- Health and Safety Executive website for information on regulation of pesticides
- Further NRW information on biosecurity