If you get knotted…is there a way out?
Top of the Environment Agency’s list of most wanted foreign species is Japanese Knotweed and in the front line attack against it is a company with roots in the High Peak. Mike Clough, from Glossop, formed the first company in the UK to recognise its problem potential seven years ago, Japanese Knotweed Solutions Ltd. Alex Dayes, joined two years ago as environment conservation graduate and is now senior surveyor. He lives in New Mills, although he was brought up over the hill in Mellor, and has always enjoyed being outdoors, counting fishing, and mountain biking among his interests, so his commitment to combating the pernicious plant is both personal and professional.
‘Japanese knotweed was introduced into this country in the mid-nineteenth century as an ornamental garden plant. Some local authorities even planted it in an effort to stabilise water courses and railway embankments,’ Alex explained. He acknowledges the visual appeal of the tiny frothy white flower spikes in late summer, the neat heart shaped leaves and brightness of their spring green to autumn yellow colour, but is not fooled by its innocent appearance. This is a highly undesirable alien. ‘It pushes out our native species and impairs the habitat for wildlife, adding nothing to the bio-diversity, and it has no particular ecological value. It can grow 10 cm a day, to about 3m high, in any type of soil and is considered to be the most invasive plant in Britain. The Wildlife and Countryside Act of 1981 makes it an offence to plant it or cause it to grow in the wild.’
‘We only have the female plant in this country so it reproduces through rhizomes, the root-like underground stems, which can spread up to 7m away from the parent plant and up to six feet deep. A piece of rhizome as small as a finger nail is enough to set off a new plant, or stand. You often see it near water, as fragments are easily disturbed when a stream swells and soil is swept down the river, distributing the rhizomes along its course. How quickly a stand spreads depends on the micro-climate – I know of some on high ground that are fairly compact, but in sheltered areas they multiply quickly.’
Japanese Knotweed is as much a menace to the urban environment as to the countryside. It has infected many derelict and brownfield areas, often as a result of fly tipping. It grows aggressively – through concrete, tarmac, roads, paving – so has to be cleared completely before regeneration can begin. It threatens building foundations, drainage systems and flood prevention measures, weakening the flood defence structures, eroding river banks and reducing the ability of channels to carry floodwater away.
The armoury for Alex and his comrades is determined by the nature of the site and scale of the problem. Chemical spraying with the appropriate herbicide teamed with strict precautions for preventing spread are essential. Often you need patience to match the knotweed’s persistence - it can take five years to eradicate completely.
‘When treating a site you need to fence it off and put up notices explaining the work, install footwash and wheelwash facilities, and observe the regulations for removing or disposing of contaminated soil, which is controlled waste. You can’t rely on burning knotweed - in Japan it grows on the mountains in volcanic ash, so heat is no guarantee of destroying it, and as the rhizomes can lie dormant for up to 20 years, you have to be very sure they’re dead before you bury them.’
Is this herbaceous horror a problem in Japan? “No, because it has natural predators there, particularly a root fungus that keeps it in check. Researchers are looking into whether we should introduce that here, but it might bring more problems than it solves, so for now we soldier on and due to the resilience and speed of growth on certain sites it is a losing battle. One of the main problems is complacency, so we hope everybody will do their bit – if you spot Japanese Knotweed, report it to the landowner and make sure responsible action is taken’.
Marple Review Spring 2008
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