JAPANESE KNOTWEED BASIS reg.: E/5620/ICMAH ) Japanese knotweed (Fallopia japonica) is an herbaceous perennial described by allopia invasive scientists as the most invasive plant in Britain today. This Invasive Alien Species (IAS) can grow vigorously at rates of up to 10 c centimetres per day to form dense stands up to 3 metres in height, forming impenetrable leaf canopies and mats of decomposing leaves during autumn that smother native species and lower habitat sity. biodiversity. The threat of Japanese Knotweed to native plants and the construction industry has been widely recognised and is covered by legislation surrounding its removal. handling, planting and removal In the UK it is an offence under the Wildlife and Countryside Act to ‘plant or otherwise cause the growth of the plant in the wild’. The plant reproduces vegetatively in the UK via underground rhizomes capable of extending 3 m in depth and 7 m laterally and exposing weakness in engineered foundations structures such as building foundations and underground services. This causes major delays in building projects and escalating costs for developers. The cost estimated by DEFRA to eradicate all UK Japanese Knotweed infestations was £1.56 billion. functionally Although Japanese knotweed is functionally dioecious (meaning a plant species with separate male and female individuals) in its native Asia, only female plants have been recorded in so far in the UK. However the plant is proving a successful invader small despite this, with rhizome fragments as small as 0.7 g in weight potentially developing into a new infestation. Dispersion of Japanese Knotweed is by transportation of rhizome fragments in wind, along water courses and by animal movement. However, it is mainly anthropogenic onveyance activities such as the conveyance of contaminated soil material by plant and other machinery that contributes to the successful invasion of this species on development sites. This highlights the imperative importance of strict hygiene procedures during zones works within contaminated zones to prevent spread of the plant to the wider site. FOR CONTROL AND MANAGEMENT OPTIONS PLEASE SEE OVER F ONTROL Control and Management 1. Environmental Clerk of Works The most cost effective solution to a Japanese Knotweed infestation where the plant is unavoidably associated with proposed earthworks or a building footprint is the provision by an appropriately accredited company of an ‘Environmental Clerk of Works’. This service zones. provides specialist advice and supervision of activity within contaminated zones. Developers are able, under supervision, to utilise their own plant and operatives, significantly reducing cost and disruption to build timetables whilst complying with their ‘Duty of Care’ obligations and law as it is stated in the Wildlife and Countryside Act. Following excavation, the Environmental Clerk of Works can provide advice on reducing landfill costs pre-prepared area for or supervise relocation of contaminated material to an on site lined burial pit or pre chemical surface stockpiling and subsequent chemical treatment followed by final reincorporation into soft landscaping. 2. Chemical The main method of effective control against Japanese knotweed is by excavation and/ or translocatory chemical herbicides. Chemical treatment is successful over time and, dependant killed on the herbicide used the plant may be killed within one growing season. However sensitive waterside sites and those with protected trees may take up to 5 years to clear of the plant, using non persistent chemicals to preserve the environment. y By law all chemical treatment must be performed by NPTC qualified spraying operatives and it is recommended that practitioners are qualified to BASIS level, a presently voluntary indicator of service become quality and environmental compliance which is likely to become a valuable benchmark as economic conditions tighten and the offering of ineffective ‘quick fix’ solutions becomes more tempting to less scrupulous operators. 3. Excavation Excavation and removal to licensed landfill is the most effective method to achieve complete and immediate eradication, however this can prove prohibitively expensive, especially with the upcoming phasing out of landfill tax exemption for contaminated soils soils. Selective excavation of areas of growth only associated directly with building activities in conjunction with chemical treatment will limit time delays and costs associated with removal of material to landfill, while keeping client operations in contaminated areas within the law; thus allowing developers to bust develop a more robust build timetable. Other methods such as encapsulated burial on site and formation of stockpiles of material on root deflecting barriers, followed by chemical treatment over a period of months before reincorporation into have development soft landscaping hav also proved successful. 4. Biological Control Recent research has indicated an important role for biological methods of controlling Japanese Knotweed, especially on environmentally significant and sensitive sites not intended for commercial development. Presently such research is concentrated on fungal pathogens and beetle predators of bio-control the plant and although as yet no effective bio control strategy is commercially available ADK is h working alongside CABI in this area. ADK would be interested in working with clients on sensitive sites with their University backers as field trials for potential bio control management measures. For further information on Japanese Knotweed remediation, contact Dr Emma Morley by environmental.co.uk phone on 01524 510599 or by email to firstname.lastname@example.org to discuss individual site requirements and timescales.