Ragwort thrives on wasteland, road verges and railway land and from these locations it can spread to pasture. Poor quality and poorly managed horse pastures are particularly susceptible to ragwort infestations.
Closely growing grass sward prevents ragwort growth but when the grass becomes thinned out, due to poaching or over-grazing, the seeds are able to germinate in the exposed soil.
Most animals will avoid eating ragwort as long as they have an alternative source of good food. However, this can be a problem on sparse, overgrazed pastures where ragwort can thrive.
There are some anecdotal reports that some horses can develop a taste for the plant, especially if there is little else to eat.
When cut or wilted during hay or haylage-making, ragwort loses its bitter taste and becomes more palatable to horses.
Because the drying process does not destroy the toxins, dried grass, hay and haylage are common sources of ragwort poisoning.
Ingestion of the pyrrolizidine alkaloid toxin contained in ragwort typically results in the delayed onset of chronic, progressive liver failure.
Cases of poisoning occurring in late winter and spring often result from the feeding for some months previously of hay or silage cut from ragwort-infested swards.
Ragwort Life cycle
Ragwort germinates in the autumn (mainly) and spring and its seeds can take hold anywhere the soil surface is exposed and conditions are favourable.
In grassland situations, this can be due to poor sward establishment, poaching and over-grazing. Ragwort does not tolerate regular soil cultivation and is rarely a problem in arable fields.
Ragwort is a biennial plant, taking two years to fully grow and flower. It grows from seed and remains in the dense rosette stage for the first growing season. In the following year, it produces its familiar golden yellow flowers on a stem varying in height from 45cm to 75cm.
Flowering normally takes place in late summer. After that, most plants die off leaving a gap for new seedlings. However, it is also capable of becoming a short-lived perennial, flowering every year, if the flower stem is cut or mown.
Ragwort primarily spreads by seed dispersal, but root fragments are also capable of reproduction.
Each plant produces 50,000 to 200,000 seeds over a four or six-week period between July and September. The feathery seeds are dispersed by wind, water, animals, hay and farm machinery and can remain viable for as long as 20 years, depending on soil conditions.
The only way to safeguard against loss from ragwort poisoning is to eradicate the weed either by pulling, ploughing, cutting or chemical control.
Pulling the entire plant out of the ground by hand is recommended where infestation is not severe and labour is available. Pulling after heavy rainfall when the ground is soft gives best results but this should be done before seed has set. Pulled plants should be removed and destroyed by burning. Because the seedling and rosette stages are not usually removed by hand pulling, the operation should be repeated for two consecutive years to achieve satisfactory eradication.
The most reliable method of control is to plough infested grassland and follow with a three or four-year rotation of arable cropping before establishing a good ley again. Unfortunately, this can only be done in areas which can be tilled and where arable farming is practised. Ploughing followed by direct seeding will not be a success unless chemical control (2.4DB or MCPA) of newly germinated ragwort is carried out in the new ley. Extra care should be taken to prevent the development of seeding ragwort in new ley.
Cutting the plant before the flowers are open prevents the weed from seeding and spreading, but it is only of limited value unless carried out over a number of years and accompanied by good grassland management. In some cases cutting can induce development of several heads and the affected plants may persist as perennials. Cut plants should be collected and destroyed as an additional precaution against the risk of seed formation and livestock poisoning.
Herbicides work best on ragwort in the rosette stage. Ragwort plants become more palatable after spraying and consequently livestock must be kept off treated fields and fodder conservation delayed until all plants are dead and sufficiently rotted down.
In these circumstances, spraying should be carried out during late autumn (mid-September to mid-November) or early spring (mid-February to mid-March).
Either 2.4D or MCPA formulations may be used for spraying during this period. However, the 2.4D, ester formulation, works best under colder conditions. Any plants surviving a winter spraying operation are very stunted and weak and can easily be eliminated by a second spraying or by pulling.