Japanese knotweed was featured on BBC Gardener’s World (28 September 2018, episode 26) and heralded as one of the most pernicious weeds in the UK. Following on from their article, we discuss the points they raised, giving valuable information to home owners or land developers alike.
What is Japanese Knotweed?
Japanese knotweed is a non-native invasive perennial weed. It is native to East Asia in Japan, China and Korea. Its aerial growth is in the form of canes with large shovel-shaped leaves growing alternately in a zig-zag pattern. Underground, its roots and rhizomes (underground stems) can grow to a depth of 2m and laterally up to 7m.
Why is Japanese Knotweed a Problem?
Japanese knotweed has only become a worldwide menace since leaving its natural environment in Asia. In its native habitat it is kept in check by natural means; in Japan at least 30 species of insect and 6 species of fungus feed on the plant. Outside of its natural habitat these species do not exist, and with no natural predators, the plant is thriving. Growing to 10 or 12 feet high in the UK, the aerial growth produces very dense cover over a wide area, preventing native flora and fauna from growing and thus reducing the ability of indigenous, native plants from growing.
Only the female version of the plant is present in the UK, so it does not produce viable seeds. The plant possesses a strong underground stem (rhizome) system from which the plant can propagate new growth. For this reason the plant material and soils containing knotweed rhizome, is classed as special (controlled) waste if removed from site, and must be transported by registered waste carriers and disposed of at a specially licensed landfill facility.
Japanese knotweed rhizomes can cause problems underground, comparable to other woody plants and trees, damaging drains, tarmac, patios and block paving. It also has the potential to exploit existing weaknesses in walls and foundations.
The underground rhizome system can spread for several meters surrounding the aerial growth of the plant. This creates large areas of ground which cannot be disturbed due to the risk of spreading the plant. In residential situations this creates a loss of amenity use and on development sites large areas and volumes of soils which require remediation.
UK law states that you must not cause Japanese knotweed to grow in the wild and if you have Japanese knotweed on your property, you must not allow it to spread into neighbouring properties. If Japanese knotweed on a neighbouring property is causing an owner loss of amenity of their property, the owner can claim for private nuisance and be compensated for both the cost of treatment and the loss of amenity caused by the Japanese knotweed (Williams & Waistell v Network Rail Infrastructure Ltd  EWCA Civ 1514).
Wildlife & 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, e.g. strimming, flailing or dumping contaminated material, may constitute an offence.
Environmental Protection Act 1990
It is an offence under the Environment Protection Act 1990 to deposit, treat, keep or dispose of controlled waste without a licence. The Act aims to reduce or eradicate harmful acts of waste crime, such as fly tipping. This Act exists to ensure responsibility is taken by the producers of waste (such as Japanese knotweed) for managing their waste and avoiding harm to human health or environment.
How can you Remove or Treat Knotweed?
There are two methods for remediating knotweed.
- Control via Chemical/herbicide treatment
- Eradication via Excavation
Often the most cost-effective Japanese knotweed treatment and control method is a Herbicide Treatment Programme (HTP) and it will satisfy most mortgage lenders. An HTP involves methodical and carefully managed visits where the correct use of chemical over a sustained period will exhaust the plant from producing aerial growth and preventing its natural spread.
It is important to note that herbicide will not remove the rhizome from the ground. A university study has found that in most cases herbicide will not completely eradicate the rhizomes viability, meaning it has the potential to regrow following treatment, especially if disturbed.
Therefore where there are plans to disturb knotweed contaminated ground ( e.g. landscaping, building, construction works, house extension, etc) the knotweed should be excavated.
Excavation of the knotweed provides complete eradication of the affected area by removing the above and below ground plant material. The excavated waste can be removed from site to landfill, or be buried or relocated on site in accordance to industry codes of practice.
Excavation of knotweed is used when there is planned change of land use (i.e. development), or where it's undesirable to have a long term herbicide programme, or where it's undesirable to have an area of a property with restricted use due to the presence of rhizome.
When Should you call in the Professional Knotweed Company and Why?
Selling or Buying a House
The Royal Institution of Chartered Surveyors (RICS) produced guidance in 2012 to assist surveyors and lenders in understanding the procedures that should be followed where Japanese knotweed is discovered. There are four categories ranging from knotweed being more than 7 metres away from a neighbouring property (category 1) to category 4 where knotweed is within 7 metres of the inhabitable property.
As a result, a question was added to the Law Society Property Information Form (or a "TA6") in 2013 asking if the property is affected by Japanese knotweed. This is because mortgage lenders want to know if the property has knotweed growing on it, or close to it, as this is perceived as a risk.
Developing a Site
When disturbing knotweed contaminated soil, the Environmental Protection Act of 1990 states that you have a duty of care to control the knotweed, handle and dispose of the waste legally.
- Prevent spread offsite and around the site
- Prevent spread onto site
- Develop an optimal Knotweed Management Plan, minimising damage to the environment, existing built structures, socioeconomic impacts and quantity of waste generated
- Provide detailed reports of Japanese knotweed control work
- Provide a company guarantee with Insurance Backed Guarantee
- Provide upfront costs with a breakdown of what work is included
Tackling the Problem Yourself
Some people affected by Japanese knotweed might feel they can tackle the problem themselves, either through chemical treatment or through digging it out. You are under no obligation to use an accredited Japanese knotweed remediation company.
However, when you want to sell your property, or if a neighbour subsequently claims for knotweed encroachment, you will be required to employ the services of a specialist knotweed company, such as Japanese Knotweed Ltd. The specialist will perform a knotweed survey, a professional treatment programme with company guarantee and Insurance Backed Guarantee.
Whilst digging out the knotweed sounds like a simple task, from experience, we can tell you it’s not. We would always recommend that a professional company is used so that the knotweed problem is tackled correctly, without further contaminating the land or neighbouring land and ensuring that the problem is gone for good.
The Knotweed Solution
The best solution to dealing with knotweed is to call the experts. We have years of experience in dealing with knotweed in many different locations and situations.
If you think you have knotweed on or near your property, contact us; we can help.