Japanese knotweed and local councils

Daniel Docking of the Property Care Association (PCA) explains best practice for local authorities dealing with Japanese knotweed

The effective management of Japanese knotweed has become a top priority for many councils. Dubbed as one of the most invasive plants in the world, Japanese knotweed can be found in every county of the United Kingdom, and its notoriety has been gained mostly due to its presence within the built environment, affecting a homeowner’s ability to obtain mortgages from financial institutions and its alleged destructive capabilities.
    
As this invasive non-native plant is tied to legislation, we have seen a rise in nuisance cases due to mismanagement and/or encroachment. This is forcing individuals, organisations, and councils to responsibly manage infestations, creating a significant strain on finite resources and shrinking budgets.

A legal responsibility
A common misconception is that it’s illegal to even have Japanese knotweed present on your land. This is not the case; however, councils do have a legal responsibility to manage invasive species within their areas of jurisdiction. This core responsibility is outlined in the Environmental Protection Act 1990 and Wildlife and Countryside Act 1981, and under Section 14(2) of the Wildlife and Countryside Act 1981, it states it is an offence to plant or cause Japanese knotweed to grow in the “wild”.

A growing problem for many councils
Councils have a duty to ensure that Japanese knotweed is managed effectively to prevent it from causing harm to the environment, property, and infrastructure. A recent court case in 2023 Davies Vs Bridgend County Borough Council, only further highlights the importance of managing Japanese Knotweed.
    
In summary, Mr Davies sought legal action against Bridgend Council, where it was deemed that the respondent was in breach of the relevant duty in nuisance owed to the appellant as a neighbour, starting from 2013 until 2018 when a reasonable and effective treatment programme finally started. Although an expert identified Japanese knotweed being present on the respondent’s land for over 50 years prior, Bridgend Council failed to take any reasonable action in reducing the spread of the plant.

Impact on the built environment
Japanese knotweed has the capability of spreading from roughly a thumbnail size of rhizome. The plant’s strong and extensive root system can penetrate small pre-existing cracks within concrete, tarmac, retaining walls and other materials, causing further damage as it grows and exploits these weaknesses. Japanese knotweed often grows in areas that are difficult to access, such as waterways and river embankments. Soil erosion can dislodge active rhizomes, where it will continue downstream, creating a new infestation and creating a continuing cycle or reinfestation along the river embankment.
    
If Japanese knotweed is identified on council-owned land, financial institutions may consider imposing lending restrictions, resulting in difficulty in selling or leasing the land until a suitable management plan is implemented. Costly repairs, potential lost revenue and environmental impacts are just a few considerations for councils when setting goals to actively manage this invasive plant, which currently costs the UK economy a staggering £165 million per year.

An established invasive weeds industry
Despite the challenges posed by Japanese knotweed, there are some grounds for optimism. A maturing specialist Japanese knotweed industry, established in the early noughties, has seen a rise of trained experts capable of tackling this invasive plant. Plant identification apps have helped to increase awareness of the issue to encourage more people to report sightings of Japanese knotweed and help prevent the further spread.

Strategies for managing Japanese knotweed
There are several strategies which councils can adopt to manage Japanese knotweed successfully.

Early Detection & Rapid Response
Implementing an Early Detection and Rapid Response (EDRR) is an approach aimed at identifying and treating Japanese knotweed before it has the opportunity to spread. This involves training staff or using specialist companies with qualified surveyors (Certificated Surveyors in Japanese knotweed) to identify and implement a process for reporting and responding to sightings of the plant.
    
EDRR is especially effective in areas where the plant may be at a high risk of spreading due to ground maintenance, high public foot traffic, or in areas which are unlikely to be developed such as roadside verges or public open spaces.

Biosecurity measures
Implementing appropriate biosecurity measures will reduce the likelihood of potential spread by fencing off an area where Japanese knotweed is present, and signposting will raise awareness of its presence to the public or council workers. This can reduce the overall long-term cost and by creating a proactive response to a successful identification, should be considered as a priority.

Surveys & site-specific reports
An invasive species survey is recommended for any development project at its pre-construction phase to establish the presence of any invasive plant which could later affect the project. It’s vital these are conducted by competent CSJK surveyors who have the specialist skills and knowledge to be able to identify any invasive plants. A site-specific report will provide suitable remediation solutions which are applicable to the project needs and timescale.

Herbicide control
Once infestations are identified, a crucial task is to manage these areas. Herbicide control is a cost-effective strategy for managing Japanese knotweed and can be effective if applied correctly. Using this approach should be carried out in conjunction with an Integrated Weed Management ethos, creating a sustainable approach where herbicides are used to target specific plants in an extremely controlled manner.
    
Using competent and trained professionals with the PCA Qualified Technician (PCAQT) in Japanese knotweed, should be considered as the minimum requirement for individuals undertaking the task of managing the plant with herbicides. Overdosing or using too much herbicide within a single season can often have detrimental effects, causing the plant to enter a temporary dormancy. This will cause the plant to “hibernate” producing little or no active growth within a single season, however due to the large energy reserves within the rhizomes, a stronger reoccurrence will likely be seen once this temporary dormancy breaks.
    
Properly applied applications of herbicide over a several year period will reduce the plant’s capacity to spread by slowly removing the large energy reserves within the rhizome. Furthermore, it will reduce the plant’s capacity to cause damage to any built or landscaping features and further reduce the negative impacts on the environment. This management strategy does not remove the plant and its propagules from the soil, but simply manages it in situ, leaving restrictions on-site if there are future developments.

Excavations
Excavations can provide an alternative method for addressing Japanese knotweed, although not as cost effective in comparison to herbicide control. This strategy involves removing the rhizome from the soil and carting any contaminated material away to an EA approved landfill. Complete removal comes with a high price tag; although various possibilities are available, all excavation options require a high level of speciality and should only be undertaken by approved Japanese knotweed contractors.

Japanese knotweed is manageable with the right help
As we said earlier, Japanese knotweed is manageable, but failure to successfully control this plant can cause severe economic and environment damage, with significant resources absorbed by it. Recent innovations have led to the use of sniffer dogs in identifying the smallest amount of rhizome on site, and drone technology has made previously inaccessible embankments viable for surveillance.
    
Whilst this may be looking somewhat into the distance for many local councils, for now, implementing EDDR strategies and the help of specialist experts, will provide local councils with opportunities to recapture land which may have been lost to this non-native invasive plant.