Japanese knotweed (scientific name Fallopia japonica) is sometimes known locally as 'donkey rhubarb'. It first came to the UK in the mid 19th century as a garden plant. Since then it has become a serious problem. Particularly on roadsides, riverbanks and derelict land. It prevents our native plants from growing and causes structural damage. In the photo on the right you can see knotweed growing through concrete blocks.
In the UK it mainly spreads by roots or parts of the root or by the base of the stem or stem pieces.
The majority of Japanese knotweed has been spread by by mans' activities. These include fly-tipping garden waste and moving contaminated soil. Mechanical flails and mowers will also spread the plant.
In Cornwall Japanese knotweed has become widespread. It is a significant problem making it difficult to restore or develop land. It spreads very easily from tiny parts of the plant and it is very difficult to control. It is also therefore an expensive weed to manage.
Why it has become a problem
Japanese knotweed is not native to Europe. The pests and diseases that control it in Japan are not present in the UK. In Japan it grows in harmony with other plants and only grows to a fraction of the size that it does in the UK. Similarly, many British plants that have been taken abroad have become highly invasive elsewhere.
Japanese knotweed is a problem throughout Europe and most of North America. It stops the growth of almost all of our native species, which cannot compete with the tall summer growth, or the thick mulch of decaying canes and leaves in winter. Many of the insects that are dependent on our native plants are also lost.
Report Japanese knotweed on Cornwall Council land
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The information on these pages has been compiled by the Cornwall Knotweed Forum from information provided by its members and partners. It is provided in good faith to the raise awareness of the issues and to promote best practice in the control of Japanese knotweed. The information may be used freely for private and educational purposes but may not be copied for commercial use. We update information and advice on a regular basis. However the Cornwall Knotweed Forum, or any of its constituent members cannot be held responsible for the efficacy of the treatments described, or any damage to persons, property or the environment that arises from interpretation of the advice given.
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