I am supposing your fruitless plum is Purple Pony Cherry Plum (Prunus cerasifera). At any rate, I am sure it is a member of the genus Prunus which includes peaches, plums, apricots, cherries and chokecherries. P. cerasifera is not listed specifically in any poisonous plants database, but many other members of the genus are listed and all have the same warning about the ingestion of leaves, twigs or seeds of fruit. These parts of the plants contain cyanogenic glycoside or cyanogens that are highly toxic and may be fatal if eaten. Cyanogenic glycosides are changed into free cyanide either in plant material that has been damaged or in the gastrointestinal tracts of animals. It is most severe in ruminants (cattle, sheep, goats, deer) but is also very dangerous for animals with single stomachs (e.g., dogs, cats, horses, pigs).
See the following poisonous plants websites for information about the Prunus spp.:
If there is a Prunus spp. tree in the field where the horse is to be pastured, I believe I would remove the tree or move the horse to a different pasture. This is especially so if it is a small pasture where the horse is more likely to come in contact with the tree or if other vegetation is sparse so that the horse would consider eating leaves off the tree.
More Poisonous Plants Questions
Are leaves of banana trees poisonous? August 10, 2008 - are the leaves of banana trees poisonous? the tree will be in a preschool classroom How do i care for the tree? view the full question and answer
Are berries from the Carrot Wood Tree toxic to animals? May 26, 2009 - Hello, I am trying to find out if the berries on the carrot wood tree are toxic to animals - dog? view the full question and answer
Living fence line from Thomasville GA November 04, 2012 - I would like to create a natural fence line on my property in South Georgia. They need to be pretty dense and horse, cow, goat friendly, growing to a height of about 4ft, preferably quickly! Do you ... view the full question and answer
Plants Toxic to Horses October 26, 2013 - I want to put planters on the front of my horse barn, which is also in the front field, so the horses could eat what is in it if they want to. I am looking to put a miniature pine tree in the planter.... view the full question and answer
Wild plums for jelly from Conroe TX December 18, 2012 - Do wild plum trees grow in my area? I want to get some next summer to make plum jelly. view the full question and answer