Japanese Knotweed Survey

The Wildlife and Countryside Act (1981) / Wildlife (Northern Ireland) Order (1985) made it illegal to spread Japanese Knotweed (JK). Its propensity for rigorous growth is a potential risk on development sites, where its presence can damage structures and impede landscape developments. Early identification of JK allows a developer to include options and costs for appropriate management (remediation/treatment/disposal) so as to avoid excessive cost, potential prosecution and prevent physical damage to buildings and hard surfaces.

At TGEN we recommend a holistic approach to the investigation of sites and therefore where required a JK Survey can be combined with other investigations such as a Phase 1 Preliminary Risk Assessment or a Phase 2 Site Investigation to minimise overall costs and allow a coordinated strategy for remediation to be developed based upon the proposed construction plan to ensure that the most efficient strategy is developed.

Works undertaken as part of a JK Survey would include the following:-

  • Mapping of the site in order to determine the current location and extent of the JK infestation(s).
  • Provision of a legal, environmental and risk assessment of the infestation at the site.
  • Provision of a photographic record of the infestation.

Based on the findings of the survey detailed options for the treatment/remediation of the JK would be outlined, which would include:-

  • Findings form the survey.
  • Recommended treatments based upon the extent of infestation, location, project timescales and project budget.
  • A schedule of works together with a full breakdown of costs.
  • Identification of risk of contamination and infection from external boundaries around the site.
  • Detailed method statement for the chosen treatment.
  • A management plan for the protection of the infested area and the prevention of any further contamination, therefore minimising the risk of prosecution.

There are several options available for the management of JK:-

  • Stem Injection - involves injecting a concentrate of glyphosate herbicide into each cane of the weed using specialist equipment specifically designed for the treatment of JK. Stem injection programmes typically require three visits over a 12 month period to complete.
  • Foliar Spray Treatments - using a glyphosate based concentrate can be completed to allow the weed to absorb the herbicide through the leaves. This takes time for the plant to transport the herbicide down to the rhizome (root crown) to ensure no re-growth occurs. A number of treatments will be needed to make sure this is effective and may take a minimum of 24 months to complete.
  • Dig & Dump - involves digging out to a depth of 3m and 7m radius around each infected area. All waste material including rubble and soil must be treated as contaminated and be disposed of by a licensed haulage company and into a an appropriately licensed waste site.
  • Dig & Move On-Site - the infestation is dug out to a depth of 3m and 7m radius then, rather than being removed off-site to landfill, the infestation is moved to an area within the site (e.g. bunded) where it can be treated at a later date.
  • Burial On Site - is available when other options are not viable and no land is available for on-site treatment. It is also a more cost effective method than removal off-site.

During any works as per The Knotweed Code of Practice published by the Environment Agency (2006), the infestations would be fenced and signposted in order to prevent further spread of the infestation, either on or off-site. This will also prevent any damage to the plant that can delay the implementation of, or increase costs associated with, any remediation programme.

If you would like further information on JK Surveys either as a stand alone service or in conjunction with any other of our services then please contact us at info@terragenenvironmental.co.uk