Ever heard of Japanese knotweed? Well, if you’ve answered no, you might have been living in a cave since 1990 because it is the highest profile plant in the country right now and has been the subject of thousands of column inches in national/regional and trade journals over 30 years.

We’ll attempt to explain why this is and how a bit of knowledge about this plant could save you and your client some money and help you both avoid prosecution!

The knotweed ‘problem is definitely relevant to the fencing/ landscaping industry. Put simply, Japanese knotweed is a blight on property and if you are digging in and around development sites or residential areas you need to know how to recognise it and, when found, avoid spreading infected soil. Before getting to the details lets look at the background to the story.

Japanese knotweed is an ‘alien invasive’ plant species which is fast-growing and a ‘super-spreader’ (via fragments of its rhizome/root system in soil). It is resistant to all our native insect/fungal diseases and unfortunately the ones which parasitise the plant in Japan don’t survive the UK climate. As a result, since its introduction over 150 years ago, it has become the dominant ‘climax’ vegetation along many of our rivers and lakes, railway embankments and roadsides. Due to its dominance over native plant communities it is listed under Section 14:Schedule 9.2 of the Wildlife & Countryside Act which means it is an offence to plant or allow it to spread ‘to the wild’.

But the real reason for the notoriety of Japanese knotweed is its impact in urban areas. During the Victorian and Edwardian periods it was a popular ornamental due to its attractive foliage and showy flowering spikes so was much planted and shared by gardeners. Once the trend started it was difficult to stop because what most gardeners didn’t realise was that the soil for about 3m in all directions around a stand of Japanese knotweed would contain infectious rhizome fragments (less than 0.5 g is enough to start a completely new colony). We leave your imagination to work out what happened but suffice to say there are not many cities and towns around the country that do not have clusters of knotweed infested properties and, where it appears, it tends to be associated with structural damage to hard surfaces like paths/patios & driveways. Damage to building foundations tends to be incidental; it may grow-up through cavities or weakened concrete/brickwork and damage or block drains for example. An all-round nuisance!

You’d think that having identified the problem it would be relatively simply solved but nothing is ever ‘simple’ about Japanese knotweed. If you cut it down it will grow back – quickly! Most DIY herbicides are only partially effective and even professional weed control specialists need to implement long-term management plans to keep knotweed from re-emerging. If a developer wants to build houses over knotweed infected soil a fully-documented excavation/removal is needed, all conducted under strict biosecurity protocols to avoid contaminated soil being spread around the site. All ‘knotweed’ wastes arising can only be removed by a Licenced waste carriers (‘Controlled waste’) or buried/ encapsulated in-line with Environment Agency permit conditions.

These impacts have resulted in Japanese knotweed causing problems during conveyancing (difficult to sell, diminution of value) and the cause of litigation between neighbours due to so-called ‘loss of amenity’. During the 80’s and 90’s many banks and building societies started to identify a significant risk of loss-of-value/negative equity if the knotweed wasn’t managed properly and knotweed-infected properties soon became unmortgageable. Fortunately, two things happened to unlock this impasse. First, in 2006, the Environment Agency published a Code of Practice which established a benchmark for professional knotweed management. Secondly, in 2010, the Property Care Association (PCA) formed a network of specialists who could provide verified, systematic management of knotweed conducted by trained and qualified surveyors/technicians. Guarantees issued by such companies could be underwritten by insurance and this gave banks & Building societies confidence they could lend knowing that the knotweed around the property was covered by a professional ‘Japanese knotweed management plan’.

Since those early days the PCA has gone on to introduce training and qualifications specifically for Japanese knotweed surveyors (‘CSJK’) as well as for other invasive species (e.g. Giant hogweed, Himalayan balsam, bamboo).

To go back to the beginning, how is this relevant to fencing & landscaping professionals? In the course of your work you are likely to come across knotweed and other ‘invasives’ so it’s a good idea to familiarise yourself with the basic identification characteristics (Google is useful!) and avoid accidentally spreading them around either on-site or off-site (on muddy boots for example). You should also help your clients recognise where there may be a problem with Japanese knotweed etc. so they can implement management measures as soon as possible (often starting by creating a bio-secure cordon around the area). This to fulfil their legal obligations under the Wildlife & Countryside Act etc., avoid encroachment on to their neighbour’s land and prevent any damage to paved surfaces or buildings nearby.

Fortunately, to help you, the PCA website has loads of useful guidance free to access and download (see below). You can also find details of our technician and surveyor training courses and details of membership should that be of interest (many of our invasive weed group members are landscapers). If you want to work alongside a PCA member go to our home page where you can ‘find a member’ with just a postcode and then use the dropdown bar to select ‘invasive weed control’. We know that Japanese knotweed can be daunting but with the right knowledge and professional support you can give your client complete peace-of-mind.

Of course, we are here to help with any questions about invasive weeds especially if you are not sure about legal status and/or the best management approach. So, if you prefer, you can contact us in the first instance and we will try to help. Although Japanese knotweed is quite a spectacular ‘athlete’ of the plant world, its not ‘Day of the Triffids’ and we do have the tools to bring it under control.

Dr Peter Fitzsimons Technical Manager @ PCA peter@property-care.org


Fencing News Blog