The Groundsman

December 2012

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40 WEED CONTROL the Groundsman December 2012 The truth about Japanese Knotweed There are different views on how to combat Japanese Knotweed, including the cost of treatment. But, it seems, there is no 'cure all' solution The law on Japanese Knotweed is clear: landowners have a responsibility to prevent its spread into the wild (Countryside and Wildlife Act, 1981, section 14.2). But the interpretation of the law is less than clear: while the disturbance and distribution of soil containing rhizome is an issue, does allowing growth to remain unchecked constitute a crime? The critical issue is to establish the facts regarding Knotweed, and the required knowledge is not that complex or elusive. Of course, you may hear stories of crumbling new builds; an illusion that only massive spending can control the weed; unique herbicide systems that work very quickly; permanent-fix single-application methods; and no doubt many other weird, wonderful and sometimes expensive solutions. Effective treatment The truth is that all contactors have access to the same limited number of active ingredients within the choice of herbicide, which are controlled by law and are detailed in the UK Pesticide Guide and on the CRD website (www.pesticides.gov.uk). The product labels detail their suitability and the instructions need to be adhered to fully. Equally, the application itself needs to be carried out by an operator who has the correct training and certification. Only a handful of herbicides are available and some will be unsuitable for use due to the proximity of trees, other desirable vegetation or the presence of a water course. This means no 'cure all' concoctions are available. Equally, there are very few methods of application. Spraying, injection and wiping all have their place, but none provide instant success. The testing of rhizome is great but its results mean little; knowing that part of the plant is 'dead' is really no help. Digging up every last part of the extensive rhizome system and testing it would be useful; however, this surely defeats the point? In essence, unless every part of the plant is successfully treated (especially the non-visible element), removed or isolated by means of barrier materials – and this is usually possible without breaking the bank – then the problem will remain unsolved . Careful consideration of the site, its history, the planned development, level changes, timescales, buried services and previous attempts at control (or concealment) should all be considered. Sometimes minor modifications to a planned build can create the opportunity to resolve matters with ease. Comprehensive guidelines The Environment Agency has produced the document of choice to learn about what might be appropriate. Comprehensive and well illustrated, its guidelines are a useful starting point – but the guide is not totally fail-safe: there is an instruction to excavate seven metres from the edge of a stand (collection) of knotweed, but only 2.5 metres down.

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