Invasive Weed Control


Free guide: Managing Japanese knotweed

This section of membership provides consumers with a means of identifying specialist contractors and consultants who can undertake invasive weed control services which can help control and eradicate Japanese knotweed and other invasive plant species.

“Japanese knotweed is another type of ‘property problem’, in that it can be identified and treated with minimal impact.  It’s effective eradication is a job for the experts, so it’s vitally important for anyone who thinks they might have an issue to seek professional advice.”

This section of membership has been formed by a group of leading industry experts who have formulated strict criteria for PCA membership. The implementation and monitoring of these standards will provide assurance that members listed as experts in the control and management of invasive species, are capable of offering the highest levels of technical knowledge and practical skill.

Member listings and further information are now available by using the postcode ‘Find a Specialist’ section of the website.

Please see below some information about Japanese knotweed and other invasive plants which can be of concern to homeowners, managers of commercial land and premises, developers, insurers, banks and other lending agents.

Invasive Plant Species

The three non-native plants most commonly encountered in Britain that cause concern to homeowners, land owners and developers are: Japanese knotweed, Giant hogweed and Himalayan balsam.

Japanese knotweed (Fallopia japonica)Japanese_knotweed-Fallopia_japonica

Japanese knotweed has become increasingly well known in recent years, and is a growing commercial problem because of the challenges it causes in the urban environment. The plant, which is native to eastern Asia, was introduced in the early 19th century to adorn the gardens of Victorian England. As early as the beginning of the 20th century it was widely recognized as an invasive species. Where the plant grows on development sites it can cause damage to hard structures and surfaces. Developers also often need to tackle the plant in order to avoid contravening the Wildlife and Countryside Act 1981.

Japanese knotweed – Do’s

Contact the professionals. Members of the Invasive Weed Control section of the PCA are qualified and regulated in Japanese Knotweed management and can deliver efficient, effective and reliable treatment. Do not ignore Japanese knotweed when you see it in your garden or building plot. It can grow quickly and costs will grow as the plant does.

Japanese knotweed – Don’ts

  • Don’t flail Japanese knotweed as this could cause it to spread. Cutting with sharp hooks, slashers etc. or hand pulling is recommended to avoid any dispersal of cut fragments.
  • Don’t cause the spread of Japanese knotweed stem and crowns. If you cut down Japanese knotweed, it is best to dispose of it on site. Material taken off site is classified as waste and must be safely contained and disposed of at a licensed disposal site.
  • Don’t try to dig up Japanese knotweed as this will lead to a significant increase in stem density. Even a tiny fragment of the cut rhizome is capable of regeneration.
  • Don’t spread soil contaminated with Japanese knotweed rhizome. Any soil that is obtained from ground within 7 m horizontally and 3 m deep of a Japanese knotweed plant could contain rhizome. The rhizome is highly regenerative and will readily grow into new plants.
  • Don’t chip Japanese knotweed material. Mechanical chippers don’t kill Japanese knotweed. If you spread the chipped material on soil, Japanese knotweed could regrow.
  • Don’t dump garden waste contaminated with Japanese knotweed in the countryside – you will be breaking the law.
  • Don’t add Japanese knotweed to compost. Compost it separately (preferably on plastic sheeting to prevent rooting) so that you can be sure it is dead.
  • Don’t take Japanese knotweed to recycling centres that receive garden waste as it will contaminate the compost.
  • Don’t break the law. Remember, if you cause Japanese knotweed to spread you are guilty of an offence under the Wildlife and Countryside Act, 1981

See our guest blog on the TrustMark website: “Japanese knotweed – the decorative delinquent that needn’t cause panic!”


Giant hogweed (Heracleum mantegazzianum)Giant_hogweed-Heracleum_mantegazzianum

Giant Hogweed was brought in to the UK as an ornamental plant. It is native of South-Eastern Europe and is a member of the carrot family. Generally it grows near watercourses and in damp meadows, though it can be found on waste ground where conditions are right. It is a highly invasive plant that grows vigorously. Each plant can produce up to 50,000 seeds which can survive for up to 15 years. Giant Hogweed is capable of growing to a height of up to 5 metres.

Contact with this invasive weed produces a skin reaction which is antagonised by exposure to sunlight. Blisters occur 24 to 48 hours after exposure. Damaged skin heals very slowly, leaving residual pigmentation that can develop into recurrent dermatitis.

A structured treatment program using appropriate herbicides allows giant hogweed to be effectively controlled.

We have recently developed a Guidance Note on Giant Hogweed, click on the link to download – Guidance Note Giant Hogweed.

Himalayan balsam (Impatiens glandulifera)Himalayan_balsam-Impatiens_glandulifera

Introduced to the UK in 1839 from Northern India, Himalayan or Indian balsam is most commonly found on river banks and damp areas, though it is capable of thriving in many other habitats.

The dense stands on river banks impede the flow in flood conditions exacerbating flooding. They also shade out native plant species.

Himalayan balsam also causes a less obvious problem for native species. Like many flowering plants, Himalayan balsam produces a sugary nectar to attract insects. However the flowers produce more nectar than any other native European species making it more attractive to bees and other insects, luring them away from pollinating our native flowers.

A structured treatment program using both herbicides and cultural control methods such as hand pulling can provide effective Himalayan balsam control. Annual treatments are needed, focussing on early control to kill plants before they seed.

We have recently developed a Guidance Note on Himalayan balsam, click on the link to download – PCA Guidance Note on Himalayan Balsam Control.


Click here to access the Invasive Weed Control Document Library.