Practical Guidance for Dealing with Japanese Knotweed

March 10, 2017

Dealing with Japanese Knotweed can be complex and comes with a considerable cost.  According to the Invasive Species Strategy NI, Japanese Knotweed costs the GB economy £179 million per year. Indeed, just to clear a 10 acre site for the London Olympics cost a reported £70 million. Japanese Knotweed is classed as an invasive species under Schedule 9 of the Wildlife (Northern Ireland) Order 1985. Very small amounts of the plant can spread rapidly, making its removal and disposal an incredibly difficult task. Following the correct procedure for its containment, treatment and disposal is essential to avoid sanctions and protect the ecosystem and built environment in Northern Ireland.

If Japanese Knotweed is excavated and removed from the land then it becomes ‘waste’ and, as a waste, a duty of care is placed on the land owner to ensure that Japanese Knotweed does not spread to adjacent land. There is also a duty of care on all waste producers to ensure Japanese Knotweed is disposed of at a licensed landfill site and that the site operator is notified that the waste material contains Japanese Knotweed. Landfill sites also have a duty of care to prevent spread from their sites to adjacent land and must follow the correct guidelines. Great care should be taken when transferring material contaminated with Japanese Knotweed – it is an offence to cause Japanese knotweed to grow in the wild in Northern Ireland.

If the presence of Japanese Knotweed has been confirmed on a site then there are various measures which may be taken by developers/landowners in the first instance:

  • Erect signage and close area off from unnecessary interference.
  • Carry out a survey and produce a distribution map of Japanese knotweed on the site.
  • Talk to adjacent land owners and make them aware of the issues and what you plan to do. Identify potential contamination routes to your site and mitigate against these to avoid further spread/introduction of the weed.
  • Produce a detailed Japanese knotweed management plan. This may involve:
  • Long-term treatment with herbicides.
  • Excavation, deep burial and/or bunding on site prior to treatment with herbicide.

Disposal at licensed facilities can be very expensive and should be considered as a last resort. The current Northern Ireland Environment Agency policy on disposal of Japanese knotweed material and contaminated soils follows the Environment Agency guidelines. Some practical points for private landowners and developers to consider:

  • Minimise the amount of waste you generate that contains any Japanese Knotweed plants or it’s roots and rhizomes (underground root-like stems).
  • You must not dispose of Japanese Knotweed with other surplus soil. You can only reuse soil that has been contaminated with Japanese Knotweed after treatment, on the site where it is produced.
  • When you transport invasive plants and soil contaminated with invasive plants, make sure that the vehicle is covered or sheeted so that seeds and plant material cannot escape. If you allow contaminated soil or plant material to escape, you could be prosecuted and fined.
  • You must have waste transfer notes for any material leaving your site. You must list any material that contains invasive plants or their seeds on the Waste Transfer Notes. Your waste carrier can only take the waste containing invasive weeds to sites authorised to accept it ie. a site that has a pollution prevention and control permit or waste management licence. The conditions of the permit or licence must allow the disposal of invasive plants at the site. The waste site may need notice so that an area can be prepared.
  • After you’ve transferred Japanese Knotweed to the waste disposal site you must brush vehicles down vigorously or jet wash them to clear them of any Japanese Knotweed. You must also inspect vehicles to ensure there are no trapped pieces of plant or rhizome.

Ensure disposal options for plant material and contaminated soil are in place prior to work commencing and monitor for regrowth and/or reintroduction during site visits. As noted, it is an offence to cause Japanese knotweed to grow in the wild and you may find yourself the subject of civil proceedings if you allow Japanese Knotweed to spread onto neighbouring land. Indeed, even if there is a risk the weed may spread onto neighbouring land this may be an actionable interference with the use and enjoyment of your neighbour’s property. See recent case law update:

If you require any further advice on the legal issues associated with Japanese Knotweed please do not hesitate to get in contact. This article has been produced for general information purposes and further advice should be sought from a professional advisor.