Q I have heard a great deal about ragwort, a plant that is poisonous to horses. Why it was introduced to Britain? - Mary Phillips, Seaham.

A Ragwort is native to Britain and I think you are confusing it with Oxford ragwort which was introduced to Oxford Botanic Gardens from Mount Etna in Sicily in the 1700s for study.

The seeds escaped from the gardens and quickly spread along railway tracks and it is now found throughout the country.

Common ragwort (Senicio Jacobeae) is native to Britain and is a serious problem for livestock.

Many horses die as a result of poisoning from the plant.

Cattle and sheep can also be at risk. Ragwort was classified as a serious weed by the Weeds Act of 1959 and although it is not compulsory for landowners to remove the weed, the government can issue an order that enforces landowners to remove or prevent the weed where necessary.

Livestock tend to avoid eating ragwort, but where grass is scarce and ragwort is abundant, consumption may be unavoidable. If ragwort is dried and becomes mixed with hay it remains poisonous.

Unfortunately, if it is cut and left lying in a field the poison remains but it loses its bitter taste making consumption more likely.

Careful pasture management is the best way to prevent the weed and removal has to be undertaken before seed production and the plant must then be burned.

Symtoms of the effects of poisoning include restlessness, lack of co-ordination and apparent blindness.

Death can result after several months.

There is no evidence that ragwort is harmful to humans, although its management is best left to professionals.

Attempts to eradicate the plant could be disastrous to the environment since many creatures, particularly moths and butterflies rely on it for survival and they are an integral part of the food chain.

Evidence has shown that the caterpillar of the Cinnabar moth is one of the most effective controllers of ragwort as it feeds exclusively on the plant.

One possible explanation for the increase in ragwort is a plague of Cinnabar moths that destroyed much of Britain's ragwort in 1988.

Unfortunately, this meant there was virtually no food for the Cinnabar moth the following year and most of the moths died.

The moth population has been slow to recover but ragwort, by contrast, recovered very quickly because its seeds lie dormant for up to 20 years.

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Published: 28/07/2003