Buttercups

Buttercups – Are they just pretty, or are buttercups toxic to horses?

"The buttercups, bright-eyed and bold, Held up their chalices of gold To catch the sunshine and the dew" - Julia C.R. Dorr

In brief

By Kate Jewell [CC BY-SA 2.0 ], via Wikimedia Commons

Buttercups are an invasive species of weed that can not only smother out grass species but can also damage the skin and digestive tract of horses. The flowers are the most toxic part of the plant, but both the flowers and leaves are safe once the plant has been cut and dried (e.g. in hay).
Although the plant is bitter and not usually eaten, contact can cause skin problems (e.g. blistering) and if it is eaten then the horse can get mouth ulcers, colic, diarrhoea, or (more rarely) neurological signs resulting in death. This means that controlling the weed is important, even though this can be difficult to do.

More detail
Buttercups (Ranunculus spp.) flower in late spring and early summer (May-June in the Northern Hemisphere) and produce a pretty yellow flower. It is common to see photographs of horses and other animals grazing or playing in a field of buttercups, and it makes a lovely colour contrast for calendars to have a dark coloured horse cantering through a yellow field of flowers. However, even many horsey people do not realise that buttercups can cause health problems for horses, with the flowers being the most toxic part of the plant.

They thrive best in compacted wet soils with low fertility and although it is commonly thought that buttercups are a sign of low pH soils, this is not necessarily the case i.e. they also occur when the soil pH is balanced. The plant is very invasive, and can smother and replace more valuable pasture at a rate of 30-40% per year if not controlled.

By Carine06 from UK (Buttercups) [CC BY-SA 2.0], via Wikimedia Commons

What parts of the plant are toxic, and when?The toxin in buttercups is ‘protoanemonin’, which is an oily substance that forms from ranunculin when the plants are chewed or crushed. It occurs in all parts of the plant but is highest in the flowers and, because the flowers grow taller than the rest of the plant, this increases the risk of sensitive areas of the skin contacting the toxin. The toxin evaporates once the plant is cut, so buttercup flowers or leaves that are dried in hay (or cut and left to dry in the paddock) are harmless.

Some species of buttercup are more toxic than others, but it is best to control all kinds to prevent any problems and to preserve the grass sward in the paddock.

What problems can buttercups cause for horses?
Buttercups are a weed and so, like any weed, they smother out the more nutritious grass; they take nutrients that are needed for growth of the sward; and they generally lower the quality of the pasture. Of course horses that are overweight do not need a large amount of grass but control is also important prevent health problems in the horses grazing the pasture.

Health problems in order of severity:

1. Contact dermatitis: In some horses, contact with the plant (particularly the flowers) causes blistering especially if the skin is pink. This is most common on the muzzle or lower legs, but can also occur in other areas that contact the buttercups (e.g. when the horse is lying down in the paddock).
2. Digestive problems: The plant is not usually eaten because it is bitter, but if a horse does eat it then it can cause ulcers in the mouth (with drooling and reluctance to eat) and disturbances of the digestive system e.g. diarrhoea or colic.
3. Neurological problems: More rarely, eating buttercups can cause signs such as paralysis, convulsions, and death.

How do you get rid of buttercups?
Buttercups are hard to eradicate completely, however there are a number of methods that can help reduce their numbers or limit their effects.

• Spraying: various sprays will kill buttercups, but they must be used BEFORE the buttercups start to flower for a good control rate. Spraying is done when the plant is actively growing i.e. when it is in the ‘rosette’ stage with new leaves (Feb/Mar in the Northern Hemisphere). Spraying too late can lead to the flowers just going to seed anyway, although some people have success with reducing the percentage of buttercups even if they spray during flowering.
  For a recommended spray, ask at your local farm-stockist, as the type will depend on your circumstances and what other weeds you need to control. There are also some organic alternatives for those that want to avoid commercial products. Spraying will usually need to be repeated multiple times.
  Horses must be kept off the pasture for AT LEAST TWO WEEKS after spraying (or longer if other weeds such as ragwort are also sprayed). Always follow the manufacturer’s instructions!
• Cutting: cutting the flowers will remove the most toxic part of the plant, as the oil quickly evaporates after cutting. If the grass is cut as well as the buttercups, then care must be taken to keep the horses off the pasture to prevent the health problems associated with mown grass (e.g. colic). Cutting alone is usually not effective at eradicating buttercups, but can form part of a control programme.
• Harrowing: this helps to pull up the ‘stolons’ (runners) and reduces the growth and spread of the buttercup plant. As with cutting, it will not control buttercup on its own but can be useful as part of a programme.
• Removing the plants by hand: this may be possible for small areas, but is usually impractical for larger paddocks. Note that some humans have skin sensitive to the toxin too, so ideally gloves should be worn when handling buttercup plants.
• Aerating and draining the soil: because buttercup thrives in compacted wet soils, improving the soil structure will help reduce and prevent buttercups and other weeds.
• Fertilising and improving the sward. A healthy sward is better able to compete with weeds and to prevent them growing. However, many horses will put on too much weight if on rich pasture, so there may need to be a balance between fertilising to improve grass growth and ensuring the horse doesn’t eat too much.
• Protecting the horse. It is not always possible to control buttercup (e.g. in shared pasture where the owner is reluctant to use control measures), or an individual horse might need protecting while other control measures take effect. Some measures that may help include:
  • Masks/muzzles that cover the lower area of the horse’s face, without limiting his ability to eat and drink. This won’t protect the lips if the horse is rummaging through buttercup leaves looking for blades of grass, but it should help protect from the more toxic flowers.
  • Boots to cover pink-skinned lower legs.
  • Barrier cream on either the legs or face, to form a protective layer between sensitive skin and the flowers.
  • Ensuring the horses are not too hungry when they are in the affected pasture e.g. by providing hay or by feeding before turn-out. Buttercups are usually avoided because of their bitter taste, but may be eaten if the horse is very hungry.

Conclusion: Buttercups are pretty flowers, but are also an invasive weed that not only crowds out more desirable grass species but can also directly affect the health of the horse.