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Invasive species

Development advice

There are many non-native species in the UK, but only a fraction are invasive. An invasive non-native species is any non-native animal or plant which can spread while damaging the environment, economy, our health and way of life.

Problems caused by invasive species affect us all. They cost the UK around £1.7 billion annually, and their impact is so significant they are considered one of the greatest threats to biodiversity worldwide. They are regarded as a greater threat than pollution or climate change.

As well as affecting our wildlife, invasive species can affect our way of life. Some species directly affect our health like giant hogweed, while others have less apparent but just as serious effects like flooding. Several riverside and aquatic invasive plants are widely considered to increase the risk of floods. They do this by clogging water courses with vegetation, or, as with Himalayan Balsam and Japanese knotweed, by causing riverbank erosion which silts up watercourses. Sediment run-off also negatively affects fisheries and rivers’ overall ecology.

After a species’ introduction, the bad consequences and costs grow every year. In urban settings, invasive species can make residential areas unattractive and less appealing. Invasive water plants can clog ponds, which reduce their appeal, and some species like Japanese knotweed degrade built environments by encouraging vermin and littering.

Under the Wildlife and Countryside Act 1981, Schedule 9, Section 14 (as amended) it is an offence to deliberately cause invasive species listed under Part II of Schedule 9 Wildlife and Countryside Act (WAC) 1981 to grow in the wild.

Invasive Species listed under Part II of Schedule 9 WAC Act 1981 are also subject to Section 34 of Environmental Protection Act (1990) and are classed as ‘Controlled Waste’. Consequently they should be disposed of at a licensed landfill site under the EPA (Duty of Care) Regulations (1991).

Invasive plant material is considered a ‘controlled waste’. It must be disposed of according to an environmental permit issued under the Environmental Permitting (England and Wales) Regulations 2007. That is unless one of the exemptions in Schedule 3 of these regulations applies, although exemptions also require registration with the Environment Agency.

Removal and disposal of invasive species can only be done by a licensed carrier. Currently, there are no disposal sites in Bridgend County Borough.

Legal disposal

Only a licenced carrier can remove and dispose of invasive species. Currently, there are no disposal sites in Bridgend County Borough.


The maximum penalty for non-compliance with Section 14 of the WCA 1981 for each offence in the Magistrates’ Court is:

  • a £5000 fine and/or six months imprisonment and an unlimited fine subject to the court’s discretion
  • and/or two years imprisonment in the Crown Court

If these species are not disposed of correctly, a civil offence would occur which Natural Resources Wales can prosecute. Infringing the Environmental Protection Act can result in an unlimited fine.

Landscaping schemes

Landscape schemes must ensure that species listed in Schedule 9 are not included in the design.

For further advice on preferred species in relation to landscaping schemes, see the emerging Bridgend County Borough Landscape and Local Character Design Guidelines.

Guidance note one:

Where development sites have invasive plants, you must submit an invasive species management plan to the council. The invasive species management plan should be enacted for all scales of development. The plan will help developers identify the areas where the plants occur on and adjacent to the site, as well as the contamination level. The plan must include full details of a scheme for the plants’ eradication and/or control. The scheme must be approved by the council and implemented before the work starts onsite.

An invasive species management plan helps developers deal with the implications of invasive species and identifies good working practices for efficient, cost effective solutions. Also, a management plan notes the procedures for taking potentially contaminated soil off site. That would be under the provisions of:

Ecology survey

If these species are found on or adjacent to your site during the ecology survey, they should be highlighted on a constraints plan. Arrange their removal and disposal in consultation with an appropriately qualified ecologist and contractor, and in compliance with the above legislation.

Many development sites are colonised by invasive species. The most frequently encountered invasive plants in Bridgend County Borough urban developments are Japanese Knotweed and Himalayan balsam. If present or adjacent to the site, it is essential to identify invasive plant species before works begin.

Method statement

Invasive species management plans should include a method statement ensuring that everyone working on the site is aware of and adheres to good site hygiene. This can be done by:

  • marking out contaminated areas
  • ensuring that vehicles with caterpillar tracks do not work within contaminated areas where possible
  • treat contaminated soils carefully to ensure that machinery or equipment that could be contaminated is cleaned

The Independent Report Economic Cost of Invasive Non-native Species on Great Britain (2010) XCIX estimates annual costs of Invasive Non-Native Species to Wales at £125,118,000.

There are no definitive industry-wide figures for how much invasive plants cost the UK. However even on relatively small sites, control costs can be hundreds of thousands and annual UK-wide costs are likely to be many millions. The cost to eradicate Japanese Knotweed in Britain with conventional methods has been estimated at £1.56 billion.

Advice for invasive plants

There are several options for controlling and eradicating invasive plants. Advice regarding the use of appropriate options depends on several factors like:

  • the development timescale
  • the presence of nearby water bodies/land drainage
  • landscaping requirements
  • other protected species issues

Email to discuss your situation.

Before treatment

The first stage would be to identify all of the locations of the invasive species on and adjacent to the site. Then, safeguard their locations. If possible, the locations could be plotted by GPS, but it is also recommended to fence them off.

Treating commoner invasive species on development sites such as Japanese knotweed and Himalayan Balsam can be straightforward, but will involve repeat treatments to ensure eradication. However giant hogweed has additional health and safety implications that must be considered.


Showing species information where contractors access the site encourages vigilance. The Environment Agency’s identification sheets can help with this.

Developers should get advice from a suitably qualified pesticide operator or BASIS registered pesticides advisor before starting a herbicide treatment programme.

Treat Japanese knotweed

To effectively kill Japanese knotweed, infestations usually need a three year treatment programme with spraying at the growing season’s end which is normally August/September. Following the initial three years of spraying, annual monitoring visits should take place during April/May for three years. Should any regrowth be identified the annual spraying regime should be implemented.

Treat Himalayan balsam

Treat Himalayan balsam before it seeds and when the plant has put on enough growth to ingest the herbicide sufficiently. This is normally around May and early June, depending on the growing season. Himalayan balsam has a viable seed bank for about two years, and so you should consider a spraying programme of three years. Run annual monitoring visits during April/May for three years following the initial three years of spraying. If any regrowth is identified, restart the annual spraying regime.

However the most effective means of managing Himalayan balsam is before the plant flowers by strimming and, with smaller infestations, hand pulling.

Treat giant hogweed

Treatment is likely to be needed for at least five years with monitoring for a further five years. The annual treatment and monitoring programme needs a detailed schedule of works. Conduct annual monitoring visits during April/May for five years following the initial five years of spraying. If you identify any regrowth, the annual spraying regime should be implemented.

The invasive species management plan needs to include precautionary measures to avoid drift spraying that may affect a site’s native flora/fauna.

Annual monitoring followed by spraying upon identification of new growth should continue until no regrowth is identified. An ecologist should inspect the regrowth during the following growing season and instruct landscape contractors to carry out the recommended follow-up work.

An appropriate herbicide should be selected in consultation with Natural Resources Wales, and, if wildlife constraints exist onsite, the applicant’s appointed ecologist.

Should the plants be close to water, only herbicides authorised by the Natural Resources Wales for use on knotweed on/near water shall be used. A competent contractor should know what is appropriate.

Excavation can immediately remove invasive species subject to Section 34 of Environmental Protection Act (1990) and the EPA (Duty of Care) Regulations (1991). This method is suitable for stands directly affected by a site’s remediation.


We recommend that invasive species targeted by remediation works are sprayed with an appropriate herbicide, and then the weakened plants are excavated. After excavation, we recommend stockpiling or burying the contaminated material.

Excavated plant material must be carried away appropriately to minimise the risk of further infestations at the site.

Excavation of Himalayan balsam and giant knotweed

Japanese knotweed’s prime means of colonisation is through spreading its rhizomes, an underground stem system. These rhizomes can reach a depth of 3m and 7m laterally from the above ground stems. To ensure no re-growth occurs, the entire root system must be removed.

Excavation of Himalayan balsam and giant knotweed

Both Himalayan balsam and giant hogweed spread by seed. Therefore, their soil should be removed laterally and to a depth agreed with the developer’s ecologist and Natural Resources Wales.

After excavation

Following excavation, the area must be regularly monitored to identify any regrowth. Should there be regrowth, implement a spraying regime.

Vehicles used to excavate contaminated material must be washed to prevent spreading these plant species. Any water used for cleaning these vehicles should be collected. If the water is contaminated with seeds or plant material, it will not be possible to discharge it into a watercourse. Contaminated water should be passed through a settlement tank to remove any soil before a very fine mesh sieve removes seeds or plant matter.

Material sieved from water used for vehicle washing may be deposited in a controlled area of the site and monitored for regrowth.

Two options following excavation are available:

  1. The material can be removed off-site to a licenced site, subject to the Section 34 of Environmental Protection Act (1990) and the EPA (Duty of Care) Regulations (1991).
  2. It can be retained in the site in a prepared receptor area to be stockpiled or buried.

If the invasive plant material is to be retained onsite, it can be stockpiled or the bund method can be used.

If the site has areas where invasive plant material can be left for at least three years, stockpiling is possible. Following excavation, the material would be transported to and stockpiled on the prepared area to let the herbicide treatment continue.

Bunds can be raised or kept in an excavation to contain the stockpile. In either case the enclosed area needs to be large enough to hold the volume of excavated contaminated soil and be lined with a root barrier membrane. This protects the surrounding soil from unintentional cross-contamination.

Within any bunded or excavated stockpile, the aim is to concentrate the plant material in a thin upper surface of soil no greater than one metre deep. If still alive, this will enable the plant to grow in order to receive more herbicide later.

Also, we recommend that the bund or stockpiled material should receive some disturbance by being turned over after one or two herbicide treatments. The disturbance will stimulate re-growth. Then, the re-growth can be chemically treated with appropriate herbicide.

Usually, this method is unsuitable for giant hogweed and Himalayan balsam, due to the large number of seeds that may be dispersed by the wind. However if treatment occurs before regrowth can set seed, it may be suitable.

After getting the environmental regulator’s agreement, you can excavate and bury invasive plant matter onsite in a lined cell or deeper excavation.

The first method involves creating a cell, lined with a root-barrier material, below ground level. Then, the contaminated material is deposited in the cell sealed with root-barrier liner and covered with at least two metres depth of spoil and/or soil.

A burial method can also be carried out without using a root-barrier membrane. However in this case, the burial must take place below a depth of at least five metres from the finished surface. We recommend that the material containing Japanese knotweed, Himalayan balsam and giant hogweed is chemically treated before burial with a non-persistent herbicide.

Inspections of the area containing the buried material must be conducted yearly for at least three years. This will ensure no new growth has occurred through inadvertent contamination of surface material.

It is important to notify the local Natural Resources team before the burial. An inspection of the material to be buried and the burial location may be needed.

Burial on-site may need a licence under the Landfill Regulations 2002. We advise developers to enquire whether they must obtain a licence before works commence.

Also, you will need to accurately map and record the burial site’s location. This allows details to be kept with title deeds so later owners know its position. This will help prevent accidental damage and the site’s subsequent re-infestation through future works.

Brownfield sites and invasive species

Often, previous activities in particular brownfield sites can cause problems with development. The land may need decontamination before development can proceed. Integrating new development into existing urban development has control issues. An example is Policy ENV7 Natural Resource Protection and Public Health Development. It only permits proposals where demonstrably there would not be a new, or exacerbated unacceptable risk of harm to health, biodiversity and/or local amenity.

Image credit: 'Japanischer Staudenknöterich (Fallopia Japonica)' by Maja Dumat. Licence credit.

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