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Japanese Knotweed  Fallopia japonica

An attractive looking plant native to Japan, Taiwan and Northern China.  In its native habitat it is a coloniser of volcanic lava flows where it binds and stabilises soils because of the complex rhizome (root) system. Since it's discovery in the early 19th Century it has been exported all over the world as an ornamental plant and is sometimes used as a fodder crop. It is now recognised as the most invasive plant in Britain.

Japanese knotweed spreads by underground stems (rhizomes) in a similar way to bracken. It can reproduce vegetatively, <1g of stem has the ability to generate a new plant.  It grows at a rate of 5-10cm, a day reaching over 3m in height with a radial spread from its root system of 7m.  As it seeds are sterile the major cause of its spread is human activity, in particular the dumping of garden waste or contaminated soil onto the Gower commons.

It has long been used in far eastern cultures as a stir-fried vegetable and it has medicinal properties.  The flowers provide nectar for insects and it can be used as a vegetable dye.  It also has properties similar to Bracken, it can be used to stabilise soil and the canopy mimics a tree canopy providing a habitat for bluebells.

Within the UK extensive works have been undertaken to manage this species.  It is recognised as a threat to biodiversity as it dominates and often out competes existing plants communities.  Like bracken it produces dense leaf litter which suppresses the growth of those species beneath by acting like a mulch. It causes structural damage to buildings, pavements, walls and car parks as the rhizome extends to establish new shoots.

Control of Japanese knotweed is extremely difficult as it can re-grow from small fragments of stem.  These especially affect mechanical control such as cutting, pulling and mowing, because, if not properly disposed of then it will regenerate from remaining fragments.  Herbicide treatment is not effective without an integrated and repeated approach and all precautions taken. 

There are methods of biological control unlike bracken because as it is edible, especially when young, it is susceptible to grazing from sheep, cattle, horses, donkeys, and goats.  Disposal requires drying the plant out before either burning or burying off site at depth which would preclude any future regeneration. 

Japanese knotweed is included in Part II of Schedule 9 of the Wildlife and Countryside Act (1981).  Section 14 of the Act states that ‘if any person or otherwise causes to grow in the wild any plant which is included in Part II of Schedule 9, he shall be guilty of an offence’

 

   

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