Legislation
It is an offence to cause or allow Japanese knotweed to spread in the wild under the Wildlife and Countryside Act 1981 section 114 (2) (WCA 1981), as it is one of the plants listed in the schedule. All waste containing Japanese knotweed comes under the control of Part II of the Environmental Protection Act 1990.
Local councils and the police can issue Community Protection Notices (under anti-social behaviour powers) to require someone to control or prevent the growth of Japanese knotweed or other plants that are capable of causing serious problems to communities. A notice can require an individual or organisation to make reasonable efforts to make good the problems arising as a result of Japanese knotweed within a specified period of time and/ or a requirement to take reasonable steps to prevent future recurrence of the problem. Breach of any requirement of a Community Protection Notice would be a criminal offence, subject to a fixed penalty notice (penalty of £100) or prosecution. On summary conviction, an individual would be liable to a level 4 fine. An organisation, such as a company, is liable to a fine not exceeding £20,000.
It is considered good practice to check imported topsoil for Japanese Knotweed before it is accepted and used. This is to ensure that no contaminated soil is either brought onto or distributed around the site. This is particularly important for sites where Japanese knotweed has been confirmed.
There is a preference that removal of contaminated soil is be kept to a minimum, with a preference for site treatment. This is to prevent further contamination and also minimises removal of the material, which has to be undertaken by a licenced haulier as it is deemed as hazardous waste. This also helps to reduce costs.
Contaminated soil, that has been treated, can be reused but should not be taken off site except for appropriate disposal. Disposing of soil inappropriately from contaminated material is one of the ways Japanese knotweed has spread and this can lead to prosecution.
The Control of Pesticides Regulation 1986 outlines that anyone who uses a pesticide to take all reasonable precautions to protect the health of human beings, creatures and plants, to safeguard the environment and in particular avoid pollution of water. For application of pesticides in or near water, Environment Agency approval should be sought.
Consignment notes must be completed when any hazardous waste is transferred. This includes details about the hazardous waste properties and any special handling requirements, as stated by the Hazardous Waste Regulations 2005 (HWR 2005). If a consignment note is completed, a waste transfer note is not necessary. Material containing Japanese knotweed that has been treated with herbicide may still be classified as hazardous waste.
The Problem
The presence of Japanese knotweed on a development site has the potential to lead to prosecution (imprisonment of 2 years) and/or compensation claims (up to £5000), it can potentially cause damage to buildings, hard surfaces and the ecosystem of the surrounding area, swamping native and other vegetation. Due to its invasive, fast growing and persistent nature it also often reduces the value of land and properties.
It is particularly a problem once established underneath or around the built environment as it usually increases maintenance costs, therefore early detection followed by remedial work is recommended.
Photographs of Japanese knotweed (Summer months)
Early identification of its presence means that the problem can be assessed and additional costs can be factored in at the onset of a project.
Other invasive, non-native plants include Giant hogweed, Himalayan balsam, Rhododendron ponticum and New Zealand pigmyweed.
Photographs of Japanese knotweed (Winter months)
A few considerations are:
- Ensuring staff and contractors know how to identify Japanese knotweed.
- Employ a contractor specialising in the eradication of invasive weeds. The PCA Invasive Weed Group is an independent trade body recognised by the RICS and the Council of Mortgage Lenders, contractors can be chosen from a list of members.
- Choice of an appropriate control, either chemical or physical removal.
- Designating a clerk of works to oversee Japanese knotweed treatment.
- Long term monitoring after treatment.
- The more cost-effective solution is treatment in situ.
- Japanese knotweed can regenerate from fingernail size pieces of material.
- There are three main methods of control: chemical, removal and burying and trials have shown that a combination of methods proves the most effective. Early identification and control reduces cost and potential impacts on projects and the environment.
Treatment and Control Measures
In the treatment of Japanese knotweed, we can offer the following advice:
- A management plan should be produced by a specialist contractor. This includes the preferred disposal method, time scales and on-going monitoring.
- Programme sufficient time to eradicate Japanese knotweed. Records of locations should be kept, which includes locations where it is buried (if burying is the control method).
- Mowers, strimmers, chippers should not be used on any areas that contain Japanese knotweed.
- Landfill is expensive, the transport of waste material can increase the risk of spreading and should be used as a last resort.
- Reusing the treated topsoil is at risk. It is advised that distribution of treated topsoil is kept at least 50m away from any water course. It should also be kept away from areas of disturbance. This is because it may grow back and should only be used in areas where control measures can be easily administered.
- Identify and fence off areas to be treated, clarify restricted areas to public, this should include an area 7m from nearest growth.
- Vehicles with caterpillar tracks should be avoided in contaminated areas. Any vehicles leaving the site should be confined to protected haulage routes and cleaned. Material should be cleaned off these vehicles and treated in line with other waste material.
- Stockpiles of contaminated soil should be indicated and isolated.
- With due care, contaminated soil can be buried both on and off site. For offsite disposal the necessary paperwork will be required.
- Waste can be incinerated although advice should be sought through the Environment Agency.
Chemical Control
- Herbicide treatment include glyphosate, Triclopyr, Picloram or 2,4-D amine. This can be used throughout the growing season but should avoid the flowering periods to protect wildlife.
- Glyphosate was formerly the most used chemical control method for Japanese knotweed. Some glyphosate products, that also contain the co-formulant POE- Tallowamine, are being withdrawn from use by the Health and Safety Executive but glyphosate products without this additive will still be available for use. As this is a non-persistent herbicide this is often the preferred chemical for use.
- Application of herbicides should be conducted by a qualified person (NPTC). If the area is near a body of water prior approval from the Environment Agency should be sought.
- Avoid use of herbicides near water bodies to prevent harmful chemicals leaking into water bodies.
- Care should be taken if applying near trees and grasses.
- The treated soil can be reused immediately if a non-residual herbicide has been used. Soil that has been treated with a persistent herbicide may not be buried as it will contaminate groundwater, this soil should not be used within 50m of a watercourse.
- The most effective time to apply a herbicide is from July to September (or until the first frosts cause leaf fall). Spring treatment is acceptable, but less effective. Herbicides are not effective during the winter dormant stage. Chemical control usually takes a minimum of three years to totally eradicate Japanese knotweed.
- Application of the chemical control needs to be appropriate for the site, the stand size and the timescale for eradication. Chemical control can include spray, direct contact and injection application.
Burial Method
The majority of Japanese knotweed rhizome exists in the upper layers of topsoil but large buffer zones are required in order to prevent the plant from spreading:
- Burial to at least 5 meters.
- Burial to at least 7 metres from the margins of the site or any engineering features.
- Burial at least 3 metres above the base/liner of the landfill.
Root barrier systems can also be utilised to control the spread of Japanese knotweed, if burial method is adopted for the site.
One Year Solution
There are contractors who offer a one year solution. However, given the growth cycle and potential dormancy period of Japanese knotweed long-term guarantees should be sought from the appointed contractor. On-going monitoring and control measures should remain in place even if this approach is adopted beyond the 12 month period.
Management
- Ensure a clerk of works oversees all Japanese knotweed work and that all members of staff are informed of the works, controls and effected areas.
- Only disturb a minimum amount of contaminated soil and keep separate from other waste and surplus soil to prevent cross contamination.
- The control of the contaminated area usually persists for 2- 5 years. Though it should be noted that rhizomes can stay dormant for at least 20 years, even if buried. If timescales do not allow eradication, the leaves of the plants should still be treated ASAP.
- Removable of contaminated material should be coupled with herbicidal treatment on both removed contaminated soil and any regrowth from the site. This is should be conducted for approximately 3 years, until regrowth stops.
- Any recovered or disposed waste should be completed ‘without endangering human health…’ and ‘without using processes or methods which could harm the environment and in particular without – risk to water, air, soil, plants or animals…’
For further information refer to the Environment Agency’s document ‘The Knotweed Code of Practice’, 2006:
https://www.gov.uk/guidance/prevent-japanese-knotweed-from-spreading