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When non-native species such as Japanese Knotweed and Giant Hogweed become invasive they can transform ecosystems and threaten native and endangered species. Such plants can also damage economic interests, such as agriculture, forestry and infrastructure such as pipe work and drains.
Because of the threat that Japanese Knotweed and Giant Hogweed pose to native ecosystems, the Wildlife and Countryside Act 1981(as amended) make it an offence to plant or cause them to grow in the wild. DEFRA published a Horticultural Code of Practice (Help Prevent the Spread of Invasive Non-Native Species leaflet (PDF, 1.87Mb)) which listed these two plants as invasive non-native species. Although the Code is voluntary, it aims to promote a standard of reasonable behaviour that will help to ensure compliance with legislation and prevent the spread of invasive non-native species.
Japanese Knotweed (Fallopia japonica)  was first introduced to Britain by the Victorians as an ornamental plant - and was actually awarded a gold medal at a prestigious flower show! In the early spring, red/purple shoots appear from the ground and grow rapidly forming canes. As the canes grow, the leaves gradually unfurl and turn green. The plants are fully grown by early summer and mature canes are hollow with a distinctive purple speckle and form dense stands up to 3 metres high.
The plant flowers in late summer forming clusters of spiky stems covered in tiny creamy-white flowers. These provide a good source of nectar for insects. The seeds are rarely fertile and the plant spreads mainly by vegetative means. The canes can grow from the rhizome which grows underground, from an existing crown, where previous growth has taken place, or from a cut stem. During the late autumn/winter the leaves fall and the canes die and turn brown. The canes remain standing throughout the winter and can often still be seen in new stands in the following spring and summer.
Giant Hogweed (Heracleum mantegazzianum)  is a tall, cow parsley-like plant with thick bristly stems that are often purple-blotched. It can reach a height of 3.5m (11.5ft) when the flat-topped flowers appear, and has a spread of about 1m (3.5ft). It is usually biennial, forming a rosette of jagged, lobed leaves in the first year, before sending up a flower spike in the second. After flowering the plant usually dies, but not before spreading its seeds.
Although it makes an impressive plant, it is invasive and potentially harmful - chemicals in the sap can cause ‘photo dermatitis’ or ‘photosensitivity’; the skin becomes very sensitive to sunlight and may suffer blistering, pigmentation and long-lasting scars.
However, problems can also be caused when a native species, such as the common ragwort  becomes invasive.
It is poisonous to livestock, particularly cattle, horses and sheep. Palatability of the weed increases when plants are preserved in hay or silage or treated with herbicide, its poisonous alkaloids are unaffected by the conservation process. An added problem is that livestock cannot easily reject fragments of ragwort in hay and dried and dying ragwort is more palatable to livestock than the living plant. Common Ragwort (Senecio jacobaea) is an upright plant which grows up to 100cm tall. The stems are tough and often tinged red near the base but brighter green and branched above the middle with dark green leaves that are rather tough and slightly hairy on the undersides. The flower is a large flat topped head of densely packed bright yellow flowers. The single seeds have fluffy tops that carry easily in the breeze and spread the plant across wasteland, development land, roadside verges as well as railway land, woodland and grazing land.
The Weeds Act 1959 states that the Minister of Agriculture, Fisheries and Food (now the Secretary of State for the Environment, Food and Rural Affairs – DEFRA) may investigate complaints and serve a notice requiring the occupier to take action in order to prevent the spread of certain weeds, of which the common ragwort is one.
DEFRA has produced a comprehensive range of guidance and advice on the Weeds Act and ragwort control, including a Code of Practice on how to Prevent the Spread of Ragwort and accessed via the link below:
Information on other invasive species such as Himalayan Balsam is also available from the NetRegs site.
Call the Weeds Helpline on 0300 060 1112 or use the following link to download a complaint form (complaints are not directly accepted by phone and have to be submitted on the form)
Babergh District Council does not directly handle issues relating to invasive plants, please contact DEFRA or Natural England regarding this matter.
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