Japanese knotweed was introduced into the UK in the nineteenth century as an ornamental plant. It is now a problem throughout Europe because it grows much larger - up to 3 metres high - and more vigorously - underground roots can extend up to 7 metres - here because the pests and diseases that control it in Japan are not present. Red/purple shoots appear in spring and grow rapidly. The canes are hollow and are patterned with purple speckles. Leaves are bright green and grow in a zig-zag pattern up the cane. The plant dies off in the autumn/winter but the canes remain standing and can take up to 3 years to decompose. Early treatment to eradicate new infestations is recommended. Knotweed canes can be disposed of in your own garden by composting, once the stems have dried and are dark brown in colour, or by carefully burning to make sure the whole plant is destroyed. New plants can grow from the nodes of pieces of stem left in the soil.
To eradicate knotweed use a herbicide containing glyphosate. The plant carries the herbicide down to the roots and destroys the rhizomes as well. Late summer and autumn appears to be the best time to do this. Always follow the instructions provided on the label. Wear suitable protective clothing and dispose of the packing appropriately. It can take up to 3 years of treatment before the plant is eradicated completely. Responsibility for control of knotweed usually rests with the landowner or tenant of the land.
Under the Wildlife and Countryside Act 1981 / Wildlife - Northern Ireland - Order 1985 it is an offence "to plant or otherwise encourage" the growth of Japanese Knotweed. This could include cutting the plant or roots and disturbing surrounding soil if not correctly managed. Any Japanese Knotweed polluted soil or plant material that you discard, intend to discard or are required to discard is classified as 'controlled waste' and should be accompanied by appropriate Waste Transfer documentation - use link to 'Duty of Care' in the 'See Also' box for more information. Japanese Knotweed should be disposed of in a licensed, lined landfill site. Be sure that you notify your waste haulier that the waste to be removed contains Japanese Knotweed. You should also contact the landfill site several days before any material containing Japanese Knotweed is taken there to allow a suitable area to be prepared for its disposal.
