Hertfordshire & North Middlesex Area of the Ramblers' Association
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Advice on Poisonous Plants & other invaders
Horse-owner Wendy Harrow watched her dark bay gelding Scirocco die a slow and painful death. Vets didn't at first suspect ragwort poisoning but by the time the symptoms appeared it was too late. The damage had been done when a delivery of feed arrived from a supplier who told Wendy, of Llanelli, he had been 'only 70 per cent sure' there was no ragwort in his hay.
Common ragwort is defined as an injurious weed in the Weeds Act 1959 and it is an offence to allow it to spread. A common plant found particularly where pasture is poorly maintained, it is one of the most common causes of poisoning in horses and cattle in the UK. Toxins cause irreversible liver damage and, once symptoms appear, its effects are fatal. With the plant becoming increasingly prevalent, the British Horse Society has an ongoing campaign to root out ragwort.
Common ragwort has dense clusters of bright yellow flowers on stems up to a metre tall. The leaves are dark green and irregular with ragged edges, hence the name ragwort. Walkers can help in the fight. If you see ragwort on farmland report it to the Ministry of Agriculture Fisheries and Food (Rural Development Service Office are listed in the phone book and on www.defra.gov.uk). If you see ragwort on roadside verges or railway land, report it to the local council.
Every summer the BTCV (formerly the British Trust for Conservation Volunteers) gathers together teams of volunteers to tackle ragwort. Director of volunteering Keith Mellen said: "Our aim is not to eradicate it - ragwort is a native species and a valuable plant for some insects and butterflies - but to make sure it is properly controlled in areas such as chalk downland where herbicides would be inappropriate."
Alien species
There can't be many more startling plants in Britain than the giant hogweed. Growing up to five metres, its leaves can be up to a metre across with stems as thick as your shin. A species native to the Caucasus mountains between Russia and Turkey, it was introduced here as an ornamental plant in the late 19th century. It grows well on sandy river banks where its dense leaves block out sunlight, killing any undergrowth and leaving a dead area of sand or soil that creates harmful erosion. The edges and undersides of the leaves, as well as the stems, have small hairs coated with poisonous sap and the slightest touch causes painful blistering and burns even through light clothing.
The plant should only be tackled by experts and if you come across it you should contact the Environment Agency office in the area. David Scott, ecologist at the Environment Agency in Penrith, knows all about the dangers. "This is a nasty plant to deal with. Unless you really know what you're doing you shouldn't tackle it and you would be advised to steer well clear".
Japanese Knotweed
Japanese knotweed is native to Japan, Taiwan and China, and was introduced to Europe as an ornamental plant in the early 19th century. It is a large vigorous weed that appears to have no natural 
enemies in Britain. It can colonise most habitats and is regarded as a troublesome pest in many parts of the country because of its rapid invasion and domination of habitats, which results in the exclusion of other plants. It can damage property (for example by growing through tarmac or even the floors of houses) and therefore needs to be cleared from development sites. The species also causes problems in terms of flood management. It increases the risk of riverbank erosion when the dense growth of the plant dies back in the autumn exposing bare soil. It can also create a flooding hazard if the dead stems are washed into the streams and clog up the channel. A fragment of root as small as 0.8 grams can grow to form a new plant.
While there is no statutory requirement for landowners to remove the plant from their property, because of its potential harm to native species, it is listed in the Wildlife and Countryside Act 1981, which makes it an offence to plant, or cause this species to grow, in the wild. Both the Police and local authorities have enforcement functions for the 1981 Act. In addition, Japanese knotweed is regarded as controlled waste and has to be disposed of at licensed sites or by burning on site.
Defra has a PDF file on both hogweed and knotweed: Helping to prevent the spread of invasive non-native species: Horticultural code of practice. There is a Defra guide to identifying Ragwort
The British Horse Society has a PDF guide to Ragwort:The Dangers of Ragwort
Email: walking@ramblers-herts-northmiddlesex.org.uk
