Japanese knotweed management plans on commercial sites

15th February, 2017

Nowadays, Japanese knotweed (less commonly known as Fallopia japonica) is – without a shadow of a doubt – deemed as one of the most nuisance and adverse plants to be found on construction and development sites across Britain.

Known to efficiently spread very quickly, Japanese knotweed can put a decisive halt on various housing and commercial development projects. Upon realisation time is money, it is crucial to always aim to eradicate the plant once and for all, commissioning qualified knotweed consultants.

Avoid knotweed related problems on commercial development sites

Knotweed concentrations discovered on building sites are usually the source of delays and in some cases cancellations of projects, not only accruing additional costs, but also costing you your precious time. Whether is a new residential or retail development, never underestimate the consequences of knotweed infestations – acquiring planning permissions once the invasive plant has been identified can be a nerve wracking process.

In the past, we have witnesses many cases when a piece of land designated for a commercial development has been re-sold by the agency because of knotweed-induced complications.

What’s more, knotweed rhizomes can remain dormant in infested soil for many years, without any visible influence on any natural part of the flora; hereby it is possible for knotweed to re-emerge in a previously contaminated area. This can take place even though an adequate knotweed treatment plan was successfully put in place and fully completed.

A complete excavation of knotweed is usually an obligation for sites in development and building industries, where, once identified, a Japanese knotweed infestation does not allow the project to proceed any further. Any knotweed concentration must be completely eradicated beforehand.

Even if knotweed had been discovered on the property before the on-site works commenced, it may be a planning requirement that knotweed is dug up and got rid of completely, before the site crew can proceed with any development works.

Overview of knotweed control methods for commercial sites
If soil from knotweed-infested grounds is to be excavated nonetheless, to allow for building foundations to be erected, herbicide treatment is not a feasible solution. In this case, a mechanical removal of knotweed by excavation, followed by proper licensed disposal, is the most effective solution to the knotweed problem.

If a mechanical excavation of knotweed will result in an excessive amount of otherwise fine soil being removed off-site, and will have to be substituted, physical dug-up of knotweed should be avoided. The alternative assumes, if possible, careful and long-lasting treatment of knotweed roots, which is also a less costly solution.

Machinery used for knotweed excavation should always be thoroughly cleaned after each work to prevent further spread of knotweed.

Two methods of knotweed excavation and burial can be recognised.

Excavation and on-site burial

First of all, the knotweed-infected soil and any remaining bits of the plant can be buried at least 5 meters deep beneath the ground level. Alternatively, knotweed waste can be consigned encapsulated in a membrane burial cell at least 2m below the surface of the ground.

On-site burial is a sustainable and quick method of complete knotweed eradication. However, underground burials tend to exhibit some movement in months following the excavation. Hereby, it is suggested the encapsulated membrane barrier is buried under a soft landscape area, rather than a hard surface.

Apart from mechanical excavation and burial, there are several other knotweed treatment methods that can prove successful on multiple commercial sites across Britain; listed below, these are however rather long-term solutions that require weeks before the treatment plan can be considered complete and knotweed got rid of successfully.

Methods of knotweed eradication outlined below are not exclusive of each other; in most cases, a few techniques are incorporated in a given order seasonally, or as single phases in the eradication plan.

Excavation and removal off-site

Alternatively, when on-site membrane burial is not an option, contaminated soil and knotweed material can be dug up and removed off-site, to be safely disposed of at a permitted waste disposal facility.

Due diligence in knotweed waste disposal

In line with Environmental Protection Act 1990, when excavated and taken off-site, Japanese Knotweed (and any ground soil that contains knotweed rhizomes or any other part of the plant) is considered controlled waste and can be disposed of at a suitable contaminated soil disposal facility only.

Herbicide treatment of Japanese knotweed

Traditional herbicide treatment plans last up to 5 years, therefore are not a suitable method of knotweed removal for most of development companies, which simply cannot halt their works for such a long period of time.

Estimated durance of a herbicide treatment plan: between 3 and 5 years

Foliage spraying with herbicides

This knotweed treatment method is considered the most effective (in terms of costs accrued) solution for commercial clients available on the market right now.

Before a treatment plan that involves chemical spraying is put in place, there are some aspects of the area that must be considered. The size of the concentration and extent of the rhizome system are the characteristics carefully examined when a certified surveyor visits the property; these measurements allow to decide whether foliage spraying will be a successful method in a given case.

Foliage spraying with herbicides cannot be incorporated on areas surrounded by natural fauna and flora that would also be affected by the chemicals used.

Time needed for a successful treatment to be complete: between 3 and 5 years

Stem injections

Stem injections are considered suitable for smaller infestation on industrial sites. In this method, herbicide is injected directly into stem, quickly reaching plant’s the rhizomes (roots system).

As this is carried out carefully for every single knotweed plant, stem injections are considered an environmentally friendly solution; there is no collateral damage where neighbouring vegetation would be harmed.

Contrary to foliage spraying with herbicides, high precision of applying chemicals makes stem injections a recommended method to be used near water tanks or at sensitive areas covered by preservation orders for natural fauna and flora.

Estimated time needed for a complete eradication: between 3 and 5 years

Legal cues for invasive weeds management on commercial sites

According to British law, once a developer or commercial property owner is proven to have exhibited substantial level of negligence in managing invasive weeds within the boundaries of their property, which then resulted in the knotweed infestation spreading onto a third party’s land, a company that failed to prevent this can be subject to prosecution

Standards all commercial knotweed removal contractors should adhere to:

  • Wildlife and Countryside Act 1981
  • “Duty of Care” Environmental Protection Act (EPA) 1990
  • Japanese Knotweed Code of Practice updated by The Environment Agency in 2016

There are several possible legal implications and criminal sanctions that can incur if knotweed is eradicated in a way that does not respect the legislative acts listed.

Japanese knotweed cannot be left untreated subsequently infesting wildlife areas; you can be incarcerated if you illegally dispose of knotweed (any parts of the plant or contaminated soil) off-site instead of an accredited facility.

There are possible civil lawsuits if you left the infestation untreated and it spread onto an adjoining property.

Appointing a nationwide contractor to remove knotweed from industrial sites

Appointing a nationwide knotweed contractor to remediate knotweed contamination from commercial sites has one more advantage; when multiple sites across Britain are infected, a business client saves on time needed to contract a different specialist to treat each knotweed infestation; one knotweed expert company can eradicate all infestations through their networks of local knotweed consultants.

Live tracking of knotweed projects

For each knotweed removal project on commercial site we provide access to our bespoke work scheduling and live tracking mobile app.

Japanese Knotweed Specialists have adjusted to the needs of business owners who always stay on the go, with no time to waste planning future works, while our online tracking app is easily accessible via all mobile devices. Owning to our live tracking system and immediate reporting, we put our clients in control of knotweed.


Related resources on our website:

  1. Japanese knotweed eradication methods
  2. What is the legal stand on knotweed-related mortgage problems?
  3. What exactly is the type of damage knotweed can induce on your property?
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