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Japanese Knotweed

Advice for Developers and Hauliers

This section gives specific advice on what to do if you have Japanese Knotweed on a development site including: formulating a plan of action, reducing the risks of spreading the plant, your legal obligations, treatment options and disposal.

NB: The Devon Knotweed Forum provides this information in good faith and cannot be held responsible for the efficacy of the treatments described, or any damage to persons, property or the environment that arises from interpretation of the advice given.

Advice for Developers

Development Sites

Japanese Knotweed has the potential to be a serious problem for developers due to its persistent nature and the need to comply with the law. To help prevent the possibility of breaking the law and incurring large fines it is important that you address the problem of Japanese Knotweed if it is present on site. Early identification of contaminated areas is essential. Plans must be prepared to contain, control and remove Japanese Knotweed with clear methods of working to prevent its spread.

The following advice should be helpful:

  • It is important to identify Japanese Knotweed as early as possible. A site survey can be carried out by an Environmental Consultant (look in Yellow Pages). This will help reduce the costs in the long run.
  • Discuss and agree treatment proposals with the Environment Agency if the site is near a water course (Ecological Appraisal Team for Devon 08708 506 506).
  • The works and treatment of Knotweed should be supervised and monitored by experts and ongoing survey work should be carried out. Do not break the law by allowing contaminated material to be moved off site which could result in the spread of Japanese Knotweed. Knotweed material is classified as controlled waste and should be disposed of appropriately (for advice call the Environment Agency’s Environment Management Team for Devon on 08708 506 506).
  • Don’t allow Japanese Knotweed to spread into neighbouring sites or to spread onto other sites by re-using soil. You will be liable to third party liability claims.

The following is an extract from the Environment Agency’s Code of Practice:

What to do when working in an area where Japanese Knotweed is present?

  • Japanese Knotweed contaminated areas should be clearly marked out on site. Areas that do not need to be disturbed during the works should be fenced off, allowing a buffer of at least 7 meters (from the edge of a colony) to allow for the likely extent of the rhizomes.
  • Use of tracked machinery should be limited until areas contaminated with Japanese Knotweed have been cleared and/or identified and cordoned off.
  • If tracked machinery must be used in areas where Japanese Knotweed is known to be present, then consider using a strong geotextile overlain with hardcore as a base for vehicles to travel on.
  • Areas where Japanese Knotweed has been identified should be cleared slowly, one at a time with ongoing assessment of the extent of contaminated ground. Only essential vehicles should be present in areas contaminated with Japanese Knotweed.
  • Never stockpile potentially contaminated material within 10 metres of a watercourse.
  • On leaving areas of the site known to contain Japanese Knotweed, any tracked machinery that has been used should be thoroughly cleaned within a designated area. This area should be as close as possible to the contaminated area on which the machinery has been working to avoid the spread of Knotweed. This area should be monitored in the spring for Knotweed growth and a spraying programme implemented if necessary. Any machinery used in clearing contaminated areas should be similarly cleaned.
  • Care should be taken to ensure that contaminated material is not dropped or transferred to other areas of the site.
  • Japanese Knotweed contaminated spoil should only be placed on top of a fabric/membrane in an approved, fenced area. Once the contaminated material is removed from these areas, it should be monitored for regrowth, particularly during the growing season and, if necessary, treated with an appropriate herbicide.
  • All site operatives should be made aware of the requirements associated with the removal/disposal of Knotweed in order to help limit accidental spread.
  • All haulage lorries or dumpers carrying Japanese Knotweed contaminated material should be covered.
  • Never use a strimmer, mower (without collection bucket) or chipper on Japanese Knotweed material.
  • If you are working between November and March in an area where Japanese Knotweed is known to be present, then dead shoots from the previous year can be a good indication of its location. In winter no growth is evident above ground but the below-ground parts of the plant will still be alive. Breaking up this root network and transporting either off site or around your site on vehicle tracks will spread the plant. Use the precautions outlined above to reduce the risk of spreading the plant.

Any Japanese Knotweed contaminated soil or plant material that you discard, intend to discard or are required to discard is classed as 'controlled waste' and should be accompanied by appropriate Waste Transfer documentation.

Japanese Knotweed should be disposed of in a licensed landfill site. Be sure that you notify your waste haulier that the waste to be removed contains Japanese Knotweed. You should also contact the landfill site several days before any material containing Japanese Knotweed is taken there to allow a suitable area to be prepared for its disposal. You have a Duty of Care to make sure that the waste is disposed of properly and there is an ongoing liability until it is.

Control of Japanese Knotweed

Although there are a number of options available for the treatment of Japanese Knotweed, the majority of these require a number of years in order to be effective. The two methods outlined below are the most effective in the time scales generally required by the construction industry.

  1. Spraying with Herbicide
    Spraying the plant with an appropriate herbicide is the most effective option available, however it can take several years and rarely achieves control without mechanical disturbance. Herbicide treatment can give the appearance of control but the rhizome network (roots below ground) may still be viable and disturbing the ground will cause the plant to regrow. Soil movement should not be attempted if any of the rhizome remains in a viable condition.

    Spraying can only be carried out during the growing season when there is green, leafy material present. Herbicide treatments take effect within a few weeks but control can take a minimum of two sprays in one growing season to achieve. Often, when a contractor takes control of a site, the working programme is tight and does not allow sufficient time for this method of control to be used. Even so, a spraying programme may be an option for weakening the plant before removal or treating regrowth and remaining plants in the spring.

    If spraying near a watercourse (even a ditch) then you need the consent of the Environment Agency. Anyone planning to spray a herbicide must be "competent in their duties and have received adequate instruction and guidance in the safe, efficient and humane use of pesticides." This means that the person who will be undertaking the spraying must hold a Certificate of Competence for herbicide use or should work under the direct supervision of a certificate holder. A Certificate of Technical Competence can be obtained by attending a short course at an agricultural college or similar institution. Contact the National Proficiency Tests Council for more details. See Control of Knotweed / Chemical Treatment for general advice. If working near a watercourse see Advice for Riparian Owners.

  2. Digging and Spraying
    A quicker, but expensive, method of removing Japanese Knotweed involves the clearing of above ground leaf and stem material and the removal of ground material contaminated with rhizomes. The contaminated soil can be landfilled at a licenced landfill site as ‘controlled waste’ (see Advice for Hauliers) or buried on site (see below). Soil to a depth of at least 3m with 7m around the perimeter of the Knotweed should be excavated for disposal. Care should be taken to ensure that all Japanese Knotweed rhizomes are removed - this is one situation where it pays to remove too much material. Even with great care, a certain amount of regrowth in the spring would be expected and this should be treated with an appropriate herbicide as discussed above. Make sure you prevent the spread of Knotweed fragments around the site during the works. Stems should be cut neatly near the base using cutter, hook or scythe. Cut material can be dried and burnt, however, any stems left for drying should be large enough to not be dispersed by wind or traffic and well away from a water course. Stems should ideally be dried with no contact with the soil (e.g. on plastic sheeting or wooden supporting material) and should be checked regularly for re-growth. Burnt Knotweed material should be disposed of by deep burial or landfilling.
    See Preventing Spread

    On-site burial is a good option for the material. Ideally at least one herbicide treatment will have been applied to reduce the vigour of the infective material. Digging should be as described above. Burial should be to a depth of at least 5m and the material should be covered with a geotextile layer or a heavy gauge polythene sheet prior to infilling. Ensure that the site is not dug up as Knotweed can lie dormant for many years, the burial site should be marked on a map and future owners should be notified of its presence. If on-site burial is not possible then the material will need to be disposed of at an approve landfill site and the haulier and landfill site operator should be informed that it is Knotweed contaminated material.

What to do with Japanese Knotweed - image

Remember

  • You must comply with the law
  • Breaking the law will incur extra costs (potentially unlimited fines)
  • Planning conditions could be imposed
  • Treatment can be expensive
  • Failure to treat Japanese Knotweed may result in eventual structural damage, especially to tarmac surfaces.

Further Reading:

Child, L.E. and Wade, P.M., The Japanese Knotweed Manual , Packard Publishing Limited, Chichester , 2000, 123 pp, ISBN 1085341-127-2.

Advice for Hauliers

When working with landowners or developers it is important that you check that no Japanese Knotweed is included in any material you are removing. You could potentially be breaking the law and liable for a large fine by aiding the spread of this highly invasive plant. Consider developing a policy on what to do if Japanese Knotweed is found to be present in removed material.

Any Japanese Knotweed contaminated soil or plant material that you discard, intend to discard or are required to discard is classed as 'controlled waste' and should be accompanied by appropriate Waste Transfer documentation. You should not accept contaminated waste unless you can guarantee its appropriate disposal.

Japanese Knotweed should be disposed of in a licensed landfill site (see below). Your client should inform you that the waste to be removed contains Japanese Knotweed. However, you should always check. You should contact the landfill site several days before any material containing Japanese Knotweed is taken there to allow a suitable area to be prepared for its disposal as it requires deep burial. You have a Duty of Care to make sure that the waste is disposed of properly and there is an ongoing liability until it is.

Removal from Site

  • Contaminated material should be removed from the site for disposal, unless otherwise agreed with the Environmental Regulator and client. As Japanese Knotweed is considered to be a contaminant, you can apply to Customs and Excise for a 'Landfill Tax Exemption' for contaminated soil.
  • Any bags/skips containing Japanese Knotweed or contaminated soil leaving the site should be covered to avoid spread along public highways.
  • Waste transfer documentation will be required for any contaminated material leaving the site.
  • Check with the disposal site in advance that they can receive material containing Japanese Knotweed. Be aware, the disposal site may require notice to allow an area to be prepared for this material away from the landfill liner.

Landfill sites in Devon that can receive Japanese Knotweed material:

Heathfield Landfill Site
John Acres Lane
Kingsteignton
Newton Abbot
TQ12 3GP
Tel: 01626 853522

Broadpath Landfill
Uffculm
Devon
EX15 3EP
Tel: 01884 841288
Fax: 01884 841548

Viridor Waste Management run Heathfield and Broadpath Landfill sites.

Deep Moor Landfill Site
High Bullen
St Giles in the Wood
Torrington
North Devon
EX38 7JA

Tel: 01805 623496

Takes small amounts of Knotweed material.

Devon Waste Management run Deep Moor. Telephone Devon Waste Management on 01392 666444 to discuss your requirements.

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