Project objective:
Removal of a large (100m²) of Japanese knotweed and the smaller (9m²) stand that had spread from it as part of Devon County Council’s major upgrade to the A382
Client:
Devon County Council
Location:
Beside the A382 near Stover in Devon
Type of property:
Land within a highway works corridor associated with a major infrastructure project
Background to Project
PBA Solutions was appointed by Devon County Council to carry out Japanese knotweed removal in Devon along the Ice House access road near Stover. The infestation was located within land affected by planned highway improvement works associated with the A382 corridor and required intervention ahead of construction activity.
Japanese knotweed had been established at the site for a number of years and was identified within one of the recognised Japanese knotweed Devon hotspots. Without removal, the infestation presented a risk to programme delivery, long-term land management, and the potential spread of knotweed beyond the works area.
Japanese knotweed stand on the site of the A382 works corridor
The wider scheme is a multi-phase highway improvement project. It involves realignment and widening of the existing road, construction of a new link road and roundabout, and improvements to walking and cycling routes. The presence of Japanese knotweed within the works corridor created a clear risk of spread across the wider construction site, making early removal essential.
Site Details & Client Requirements
Location and land type
The site is located along the Ice House access road near Stover, Devon, within land managed by Devon County Council. The affected area forms part of a wider highway works corridor and includes fenced access, gated infrastructure, and hardstanding features. Trees previously bordered the rear of the infestation area, with mixed herbaceous vegetation present across the site.
Reason for Japanese knotweed removal
Japanese knotweed was identified growing to the south of the access road within land required to support the highway improvement works. Its position within the works corridor meant there was an increased risk of spread through construction activity if left in place. Removal was therefore required to protect adjacent land and infrastructure, and to ensure the works could proceed in compliance with invasive species legislation.
Japanese knotweed at entrance to A382 works corridor
Close up of knotweed canes and new growth at the entrance to the site
Extent of infestation
Two distinct stands of Japanese knotweed were recorded following survey.
JK1 comprised a mature stand covering approximately 100m², with average growth of around 2.5 metres, located close to a granite entrance stone and galvanised access gates. Evidence indicated this stand had been established for more than ten years.
JK2 was a smaller satellite stand of approximately 9m², with average growth of 2 metres, likely originating from the larger infestation and established for a shorter period.
Challenges and Constraints
- Impeded Access: Large boulders within the infestation area required breaking down to safely access knotweed-impacted ground.
- Isolated Rhizome: Additional isolated knotweed rhizomes were identified during excavation, requiring responsive removal beyond initial findings.
- Additional Invasive Species: The invasive Cotoneaster bullatus (hollyberry cotoneaster) was identified and segregated during vegetation clearance.
- Adverse Weather Conditions: Periods of poor weather required careful management to maintain progress and site controls.
- Live Construction Programme: Removal works needed to be delivered in step with a multi-phase highway improvement project.
Environmental Considerations
The infestation bordered previously wooded land and areas of mixed vegetation. Preventing the spread of Japanese knotweed into surrounding land, alongside the responsible management of contaminated soils, was a key environmental priority.
Before Work Began
Before removal works commenced, a number of site-specific considerations were identified that informed the approach to excavation and disposal.
The infestation included mature Japanese knotweed with well-developed rhizome networks, increasing the likelihood that contaminated soils extended beyond visible growth. Its proximity to access routes, infrastructure, and buried services required careful planning to avoid unnecessary disturbance.
Waste classification and disposal routes needed to be confirmed in advance to support efficient excavation. Trial pits and laboratory testing were therefore undertaken to establish soil profiles and inform the removal strategy.
Biosecurity was a key consideration throughout, with the client requiring assurance that works would be delivered in compliance with waste and environmental legislation and without risk of onward spread.
Heras fencing in place around works area
Preparatory Works and Site Setup
Site survey and planning
A detailed Japanese knotweed survey was undertaken to confirm the extent of the infestation within the works corridor. Each stand was recorded, photographed, and plotted using digital survey tools and Ordnance Survey mapping to inform the excavation strategy.
Vegetation cutback and access preparation
Vegetation clearance was completed across both stand locations to allow access to knotweed-impacted ground. This enabled accurate investigation and safe access for operatives.
During clearance works, the invasive Cotoneaster bullatus (hollyberry cotoneaster), a Schedule 9 species, was identified and segregated for appropriate disposal.
Soil sampling and waste classification
Trial pits were excavated to assess soil profiles and determine the likely extent of contaminated material. Representative samples were submitted for laboratory testing to confirm waste acceptance requirements.
Pre-treatment of Japanese knotweed
Japanese knotweed was treated with a glyphosate-based herbicide ahead of excavation to weaken growth and reduce the risks associated with handling contaminated material.
Compliance and site controls
All preparatory works were carried out under appropriate risk assessments and method statements, with site inductions and toolbox talks used to brief operatives on site-specific risks and controls.
Removal of Japanese Knotweed from the Devon Site
The following activities were undertaken over a six-day period:
Survey confirmation
Prior to excavation, on-site checks were carried out across the two recorded stands (JK1 and JK2) and the wider works corridor to verify the extent of Japanese knotweed. Utility information was reviewed and localised CAT scanning undertaken to confirm the position of buried services and enable safe excavation.
Removal of vegetation and obstructions
Vegetation clearance was completed across both stand locations to allow access to knotweed-impacted ground. Fencing and other obstructions were removed as required.
During clearance, Cotoneaster bullatus was identified and segregated, and large boulders within the JK1 area were exposed and assessed.
Ground protection
Track mats were installed across the working area to manage plant movements and reduce the risk of cross-contamination.
Excavator in stockpile area surrounded by track mats
Boulder breaking
Where boulders restricted access to knotweed-impacted ground, controlled breaking was undertaken to allow excavation to proceed.
Removal of knotweed and contaminated subsoil
Mechanical excavation was carried out in a staged manner across both JK1 and JK2. Knotweed-impacted topsoil and subsoil were removed, with isolated rhizome material identified during excavation also excavated and included within the contaminated waste stream.
All knotweed material and knotweed-impacted soils associated with JK1, JK2, and the isolated rhizome material were removed to licensed disposal facilities with appropriate documentation.
Removal of Japanese knotweed and contaminated subsoil from Devon site
Site cleanup and demobilisation
On completion of excavation, the site was cleaned down and all plant and equipment were thoroughly washed. Temporary fencing and ground protection were removed, and a final inspection confirmed the site was clear of knotweed material and ready for integration into the wider highway improvement programme.
Results and outcomes
All knotweed material and knotweed-impacted soils were excavated and removed to licensed disposal facilities, along with plant material from the Schedule 9 listed Cotoneaster bullatus. This minimised the biosecurity risk of spreading invasive plants across the site and allowed construction activities to proceed with greater certainty.
- A controlled Japanese knotweed dig out removed both recorded stands (JK1 and JK2) from the works corridor.
- Knotweed-impacted soils were segregated and removed off-site to licensed disposal facilities.
- Isolated knotweed rhizomes identified during excavation were removed immediately, reducing the risk of regrowth.
- The works corridor was left clear of invasive plant material and ready for integration into the wider construction programme.
Need Support with Japanese Knotweed on a Complex Project?
Japanese knotweed can present significant risks on infrastructure, regeneration, and development projects. Managing biosecurity, waste compliance, and programme risk is essential on projects affected by invasive plants. This Devon project demonstrates how a structured approach to Japanese knotweed removal can support delivery on complex sites.
PBA Solutions works with local authorities, public-sector bodies, infrastructure clients, and commercial organisations across the UK, providing practical support where invasive species must be addressed alongside engineering, environmental, and programme constraints.
If you are planning works on land affected by Japanese knotweed, or require specialist support managing invasive species on a live project, call 0203 174 2187 or 01202 816134 to speak to our team for clear, experience-led advice. Or, click to get in touch online and provide details about your upcoming project.
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