Japanese Knotweed Control Methods: How We Do It

Control Methods

There are different control and removal methods for Japanese Knotweed and the one used will depend on different factors including; the size of the Knotweed infestation, if it is growing amongst plants and vegetation you want to keep, if it is close to a water source or if it is at a development site where work needs to be started quickly.

South Wales Knotweed Removal are experts in the control and removal of Japanese Knotweed, also referred to as fallopia japonica, bamboo or peashooter. We have many years of experience and all of the qualifications and accreditations required to control, treat and remove the invasive weed which can quickly take over an area.

All our Japanese Knotweed treatment methods are endorsed by the Environment Agency Codes of Practice and the industry trade body (The Property Care Association) and they will be tailored to suit you as the client and the property or land where the Knotweed is growing. We are happy to consider a staggered payment schedule for any work that does not involve a 3rd party, who may require evidence of pre-payment in full from the outset (mortgage lenders as an example).

Stem-Injection Method

This is an ideal method of treatment that is low impact and carries minimal risk of disrupting the growth of other plants in and around it. Stem injection is normally used for smaller infestations, particularly whereby the Japanese Knotweed has managed to establish itself amongst desirable vegetation or if it is close to a watercourse which could then become polluted if another method is used.

We inject an Environment Agency approved herbicide into the lower part of each mature stem of the Knotweed using a stem injector. The Knotweed plants need to have thick enough stems for the injection of the herbicide to be effective so younger infestations may not be suitable. The stem-injection technique we use works extremely well in dry or inclement weather conditions, however, the soil cannot be disturbed following the treatment. The stem injection method is most effective from late summer onwards and offers maximum effect when the plant is in its flowering period.

Foliar Application

Along with stem injection, the foliar spray method is often the most pursued method of treatment as long as the Japanese Knotweed can be treated over several growing seasons. The method involves the plants being carefully sprayed with an Environment Agency approved herbicide. Dependent on the size of the infestation the Knotweed is sprayed on two or possibly three separate occasions in the first year and on one occasion in subsequent years.

The foliar application method requires dry weather and the soil has to remain undisturbed in subsequent years. It is not permitted when the infestation is close to a watercourse and it is not the best method to use when the Knotweed is growing amongst other plants and vegetation that you want to keep. The method is best used in late summer and has the maximum impact when the weed is in its flowering stage.

Weed Wiping

Weed wiping is a simple method and much like stem injection it has the benefit of being low impact on other surrounding plants and foliage, meaning only the Knotweed itself will be affected and not the vegetation around it. The leaves of the plant are wiped with a sponge that is soaked with the necessary herbicide. It is a low impact treatment and can be used if the infestation has watercourses around it.

The methods use does depend on how big the area of Knotweed is and it is not suitable for large areas where it has started to take over. It is often used instead of the stem injection method when the stems of the knotweed aren’t thick enough for the injection of the herbicide to be effective.


Before & After

Before and After knotweed control

Bund / Stockpiling

The bund / stockpiling method is a quick and cost-effective method used for development sites when construction needs to start quickly and the site is big enough for the Knotweed infested soil to be stockpiled temporarily and treated.

Creating a bund or stockpiling is essentially a combined treatment method of stem injection or foliar application, followed by excavating the underground material and removing the soil and material to a different section of the site to allow the development to start. The soil is then stockpiled in an area on site that doesn’t need to be built or worked on immediately, also known as a non-critical area, preferably no higher than 500mm thick. The Knotweed is then encouraged to grow in the stockpile so it is ready for the subsequent herbicide treatment. Procedures are put in place to ensure that the knotweed infested soil is not allowed to spread to otherwise clean areas of the site or from the stockpiling.

This method is much quicker than conventional herbicide application methods, saving the developer or landowner several years. It can be done at any point when the knotweeds growth is above ground so the area can be identified and it is particularly useful on building or development sites so work can start at the original infestation area.

Cell Burial / Root Barrier

Providing there is adequate space on site, creating a cell burial or utilising a root barrier will avoid the significant cost of transporting the infested Knotweed soil and waste to a licensed landfill site.

Cell burial involves burying the Japanese Knotweed material to a minimum depth or if encapsulated buried within a geo-membrane which can be closer to the surface.

Root barriers can be installed both vertically (normally when there is a risk of cross-boundary contamination) and horizontally.

Cell burial or root barrier methods are used if there is sufficient space on-site to create an area to bury or use a root barrier system for the Knotweed. Cell burial buries the Knotweed waste to a minimum depth on-site and if it is encapsulated within a geo-membrane it can be buried closer to the surface of the ground.

Root barrier systems can be used and installed both vertically and horizontally if there is a risk of cross-boundary contamination. Root barriers are used to physically control and prevent the spread of the Knotweed. This method can be used on both construction sites and residential properties if there is a suitably sized area for it to be buried.

These methods are generally suited for development sites when building and construction work needs to start quickly.

Excavation & Removal Off-Site

The excavation & removal method is when the Knotweed and the underground soil is excavated and transported offsite to a licensed landfill site.

Although Excavation & Removal of Japanese Knotweed material off-site is a legitimate and swift control option with advantages for development sites if done correctly with the right licences, we are not advocates of pursuing this method as it raises significant logistical challenges. There is a high risk of the Knotweed spreading when transporting it and the cost of transporting the material to a designated and licensed landfill site are amongst other issues.

There is a duty of care required under the Environmental Protection Act (EPA) 1990 for transporting and disposing of Knotweed. We are, however, happy to act in a consultancy role as clerk of the works providing certain conditions are met with the landowner/developer.

The excavation & removal should only ever be used as an absolute last resort.

Excavation & Removal should only be used as an absolute last resort.

All of our Japanese Knotweed treatment and removal services are provided to homes, businesses, housing & commercial developments along with properties throughout South Wales including Swansea, Cardiff, Newport and rural locations. We also work on contracts in the West Country, as far North as Shropshire and into the Midlands & Birmingham areas.

As certified Japanese Knotweed Management Plan (JKMP) Surveyors, we provide a detailed document that shows how we as the contractor will use the appropriate methods of treatment bespoke to the property or site to control or remove the Knotweed. A JKMP plan includes information relating to the severity of the contamination on-site, an evaluation of the control options available, a detailed assessment of the risks associated with any control methods and advice on biosecurity. The JKMP is updated annually following treatment & evaluation.

South Wales Knotweed Removal provide JKMP’s for residential properties, building plots that are subject to housing development and larger-scale development projects. A JKMP is normally required if you are applying for a mortgage on a property where there is evidence of Japanese Knotweed before an agreement is made to lend the funds for the property purchase.

Our JKMP’s are supplemented with a 10-year Insurance Backed Guarantee (IBG). The JKMP ‘stays’ with the property, so if there is any future property transfer the JKMP becomes the possession of the new owner, irrespective of how many times the property exchanges hands.