CASE STUDY: RAGWORT
RAGWORT, also known as ragweed or buachaláns, was classified as a noxious weed under the Noxious Weeds Act of 1936, together with the Thistle, Dock, Common Barberry, Male Wild Hop and Spring Wild Oat. Under the Noxious Weed Act, local authorities and landowners are legally responsible for ensuring that land within their control is clear of ragwort, and are liable upon conviction to be fined. Being able to identify the weed, coupled with familiarising oneself with the life cycle is the most effective way of controlling and eradicating the plant.
Ragwort is a biennial plant and so takes two years to complete its life cycle. During the first growing season, it grows from seed and remains at the rosette stage. The more recognisable yellow flowers appear in the second growing season. Once the flowers appear in late summer, most plants die off but if the flower stem has been cut, then ragwort can become a short lived perennial.
Ragwort germinates in the autumn and spring and thrives best on wasteland, road verges and undisturbed land. Each ragwort plant can produce between 50,000200,000 seeds over a 4-6 week period which can be dispersed by wind, water, animals and farm machinery. Seeds which can remain viable for up to 20 years if soil conditions allow and seeds are the principle method of spreading the weed but root fragments are also capable of reproduction.
Ragwort is poisonous in the green and preserved state to cattle, horses, pigs and chicken and although sheep and goats appear to be less affected by the plant, there is evidence to suggest that failure to thrive may be a consequence of its consumption in these animals. In general, livestock will avoid eating ragwort due to its unpalatable nature but younger plants can taste less bitter than mature ones and in cases of overstocking and grass scarcity, consumption may be unavoidable. Evidence suggests that palatability also improves when the plant dies and the wilting process increases the soluble sugar content of the ragwort foliage. Cutting for hay is therefore dangerous but contaminated silage poses a bigger threat. The poisonous toxins can diffuse out of the affected area and can permeate the entire mass of silage. In addition, palatability also increases after spraying and so it is critical to keep livestock off fields, once treated.
The poisonous toxins in ragwort, known as ‘toxic alkaloids’, cause cirrhosis of the liver with symptoms varying from acute to chronic depending on the level of ingestion. Early symptoms in cattle include poor appetite and constipation, followed by jaundice. In horses, lethargy is a characteristic symptom.
Physical methods of controlling the weed include cutting, pulling and ploughing but by far the most effective means of control is spraying. Herbicides work best on ragwort in the rosette stage and in good growing conditions with mild weather, and no rain forecast for 8 to twelve hours. Late Autumn (midSeptember to mid-November or early Spring (February to mid-March) are the recommended times for spraying ragwort with an appropriate herbicide such as MCPA or 2,4-D.