Japanese Knotweed Excavation vs Herbicide Treatment

Japanese Knotweed | 10th August 2022

Selecting the correct Japanese control method

Japanese Knotweed is a well-known invasive weed that brings with it not only the worry of structural damage to property, but also potentially legal implications. Having Japanese knotweed present can cause huge inconvenience and even prevent property sales from going through. For this reason, homeowners, companies and public sector organisations need to consider the treatment options available to them; ranging from complete removal with Japanese knotweed excavation to a longer but cheaper solution of putting in place a herbicide treatment programme.

Immediate risks of mismanagement

  • You may be liable to criminal sanctions under both the Wildlife and Countryside Act 1981 and the Environmental Protection Act 1990 for allowing the plant to spread from your property.
  • Private nuisance claim for allowing this invasive plant to spread on to your neighbour’s property.
  • The inability to sell your property or gain a mortgage.

The inability to develop land for commercial purposes.

Whether you are a commercial landowner or private homeowner, finding Japanese Knotweed present on your property is a cause for serious concern, and will raise many questions. Prominent amongst these are:

All of these questions are important; however, in this blog we will be looking into two of the most popular solutions for Japanese knotweed control: Japanese knotweed herbicide treatment and Japanese knotweed excavation. In addition, we will cover a third less talked about, and potentially cheaper, solution of carrying out a reduced-level-dig.

Knotweed herbicide treatment

Herbicide treatment of Japanese Knotweed typically involves a long term, low disturbance, treatment control plan. The treatment process (including monitoring) can take  7 years or more but is often cheaper than the alternative excavation process. Whilst the lower cost of this method is attractive it does come with a caveat; it is not a suitable method to use where the ground is likely to be disturbed in the future.

The method involves the carefully timed application of herbicide to the foliage at suitably targeted point of the plant’s growth. Most often herbicide application is via a backpack sprayer; however, in certain circumstances (near water) individual stem injection may be more appropriate. Applications are repeated over several years before monitoring visits commence.

The cost of Japanese knotweed herbicide treatment is cheaper than excavation but this cost will vary dependent on the treatment area and the maturity of the plants. It’s a very effective Japanese knotweed control method that is ideally suited to residential or commercial sites that do not need to be disturbed by digging in the future.

Treatment consideration

Whilst herbicide treatment of Japanese knotweed is an effective control method that will satisfy mortgage lenders, it is not proven to completely eradicate or kill Japanese knotweed. A long-term study by Swansea university (1) showed that regular carefully timed applications of the herbicide glyphosate were very effective at controlling the regrowth of Japanese Knotweed but that the herbicide was not always completely translocated to the rhizome.

This means that if treatment is not repeated the Japanese Knotweed would eventually begin to re grow, especially if disturbed. It is also worth noting that of all the herbicides used in this trial the most effective was glyphosate used at a concentration only available to licensed professionals.

Whilst herbicide treatment provides an excellent solution for Japanese knotweed control, it cannot be said with 100% certainty that the plant will not return. To counter that possibility, it is recommended that you use a specialist treatment company, such as PBA Solutions, who can carry out additional monitoring and provide a 10-year guarantee against regrowth.

Japanese knotweed excavation

The excavation of Japanese knotweed is, to put it simply, the mechanical removal and relocation of all the plant material. It’s a much quicker (and more reliable) process when compared to herbicide treatment but is more expensive. The reason for that being, the material arising from Japanese knotweed extraction cannot simply be removed and deposed of conventionally. The extracted material must either be:

  • Removed to a licenced waste facility by a licenced waste carrier
  • Buried on site at a minimum depth of 5 metres
  • Securely sealed within a quality geotextile root barrier and buried at a minimum depth of 2 metres.

The cost of excavating Japanese knotweed is, much like the cost of herbicide treatment, highly variable and will depend on factors such as:

  • The size of the infestation
  • Ease of access to the site
  • The method of waste disposal
Japanese knotweed excavation

Japanese knotweed excavation

Treatment consideration

Excavation is more expensive than herbicide treatment, as waste disposal costs are high for knotweed material; however, it is a quicker more thorough method. This approach is particularly suited to areas that are likely to be disturbed in the future, such as development sites.

However, there is an interesting alternative to both…

The reduced level dig

Reduced level digging to control knotweed provides a potentially quicker and cheaper solution than full excavation. It utilises a combination of both mechanical excavation and root barrier geotextile membrane to lessen the japanese knotweed excavation depth and hence the amount of material that needs to be removed from site.

The process involves excavating the invasive part of the plant from the upper levels of soil before installing a geotextile membrane (such as CuTex) in a tray-like structure to cap any remaining material Japanese knotweed. Clean material is then used to cover the membrane and fill the remaining void.

Reduced level dig

Adding clean top soil further to a reduced level dig and the installation of CuTex root barrier

Treatment consideration

This method, used where appropriate, reduces waste away from landfill and is an economical solution when compared to full excavation. Whilst knotweed waste has a high price the total cost will be greatly reduced for this method.

Points to consider

Always use a qualified PCA registered professional when seeking advice on removing Japanese Knotweed. Make sure that you are happy with the management plan your professional provides you with before proceeding, and most importantly make sure the management plan is backed by an insurance backed guarantee (IBG).

Do you need help or advice about selecting the best Japanese knotweed treatment program? Call 0203 174 2187 or 01202 816134 to talk to one of our consultants.



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