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LONDON, United Kingdom, August 15, 2000 (ENS) - Tansy ragwort, a yellow flowered weed so feared by farmers that it is known as the yellow peril, threatens the health of countless animals unless it is kept in check, warned the UK's leading animal welfare agency Monday.
Tansy ragwort is a member of the largest genus of the sunflower family. (Photo courtesy U.S. Department of Agriculture)
The plant contains pyrrolizidine alkaloids which are toxic to cattle, deer, horses, and goats. Sheep are less affected. It causes a group of diseases called seneciosis.
The toxins impede the function of the animal's liver which will eventually degenerate, resulting in the animal's death. Many weeks or months may pass before symptoms arise because the animal may only be consuming small amounts, but damage is being done.
The yellow blooming weed is a member of the largest genus of the sunflower family (Asteraceae) and one of the most frequent causes of livestock poisoning by plants.
In one recent UK case, a young bay foal died suffering severe internal damage after eating ragwort. Despite emergency veterinary treatment the horse, which was found abandoned in the Newark area of Nottinghamshire, died from liver poisoning.
To avoid such incidents, the Royal Society for the Prevention of Cruelty to Animals (RSPCA) is urging landowners to rid their fields of the noxious plant, which is lethal whether eaten fresh or dried in hay.
"With ragwort poisoning, there is no cure and the only effective prevention is elimination of the plants before they claim more lives," said Martyn Hubbard, an RSPCA regional superintendent.
"It is essential horse owners are vigilant and landowners take action to wipe out this weed," Hubbard said.
Tansy ragwort is native to Europe and western Asia, including Siberia. It generally grows in untended pastures, waste areas and along roadsides in cool, high rainfall regions.
It grows extensively in many temperate regions: northwest India, Africa, U.S., Canada, Argentina, Australia, and New Zealand. In Oregon, where it was introduced in the late 1800s, it became the region's most noxious weed within 50 years.
Tansy ragwort has been brought under control in many areas by the introduction of natural predators. (Photo courtesy U.S. Parks Department)
It does not just harm animals, it also displaces native grasslands, creating dense fields of tall yellow flowers. Ragwort consumption rapidly reduces butterfat production in cattle, and the honey produced by bees that have gathered ragwort pollen is tainted, being too bitter and off-color to market.
Horses are more likely to eat ragwort when it is cut or wilted as it loses its bitter taste. A small intake of ragwort over a long period of time can be just as harmful as one large intake because the plant's toxic effects are cumulative.
Horses affected by ragwort poisoning may lose weight and condition, and suffer depression, loss of appetite, constipation, sunburn and jaundice.
Each plant can produce up to 150,000 seeds that may remain dormant in the soil for up to 20 years, making it extremely difficult to eradicate.
The RSPCA advised landowners to either use weedkillers or to dig out the entire plant, ensuring no root is left in the ground.
Intensive grazing by sheep, which may eat it daily without suffering ill effects, has also been used to control ragwort.
The U.S. government carried out the first biological program against tansy ragwort in Albany, California in the late 1950s. It introduced the plants' natural predators, such as the cinnabar moth whose larvae feed on ragwort foliage and flowers.
The seedhead fly, whose larvae feed on developing ragwort seeds, was released in 1966. A third insect, the root feeding flea beetle (Longitarsus jacobaeae Waterhouse), was released in the late 1960s. Its larvae feed on ragwort root crowns, stems, and leaf petioles during late autumn, winter, and spring.
These programs have brought ragwort under control but the plant's ability to thrive remains thanks to the presence of a large persistent seed bank, which is invulnerable to natural predators.
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