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Japanese knotweed (Fallopia japonica)


Japanese Knotweed is a highly invasive weed, which if left unchecked, will displace native species, and can cause extensive and costly damage to property or construction and development projects.

Under the Wildlife and Countryside Act 1981, making it an offence to allow the plant to spread. All parts of the plant, and any soil contaminated with the rhizome, are classified as "controlled waste". "Duty of care" requirements under the Environmental Protection Act 1990 must be met.

The plant is extremely difficult to eradicate; attempts to control the weed often fails by treatment with chemicals and re-growth occurs. Systemic herbicides are costly and only kill part of these extensive systems, and may even encourage the germination of subterranean buds on the periphery of the rhizome network.

It is therefore imperative that complete eradication is achieved prior to any site development. If left uncontrolled, Japanese Knotweed will spread with further infestations appearing throughout the developed site and/or surrounding areas.

Cases of Japanese Knotweed growing through structures such as tarmac roads, between joints and cracks in concrete slabs, stone walls and within cavity walls and drains are common.

In addition, the plant can regenerate from rhizome fragments less than 5 grams and can remain dormant in the soil for over four years making a professional and scientific approach to its eradication vital if 100% success is to be guaranteed.

If we are to ever find out how these plants are spreading, and hybridising and what will 'eradicate' the plant, not just 'control' it is very important to be able to identify and destroy them correctly.

ADK Environmental - Working in partnership: R&D

There are many different approaches to control but they all fit into three basic categories; mechanical, chemical and biological - and any permutation of the three. A combination of cutting and herbicide is probably the most effective, but even that can take years in long-established stands. Chemical control is expensive control, not always 100% effective and can have a negative effect on the environment.

Physical removal of the rhizome can be successful if whole infestations are accessible, but can produce large amounts of hazardous waste. This hazardous waste must then be taken to deep land-fill sites suitable for the deposition of live Japanese Knotweed rhizomes, (which is very expensive) since it is an offence to knowingly spread this plant 'in the wild' (Wildlife and Countryside Act 1981).

Due to these problems there is now an increasing interest in the use of Biological Control. ADK and Lancaster Environment Centre (Lancaster University) are working together to develop and commercialise methods for identification and control of invasive alien species.

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