Question: what are the poisonous plants for horses?
Answer: Ragwort. While ragwort has a bitter taste and is rarely eaten by horses when it is growing, when it is wilted or dried it becomes more palatable. ... 
Foxglove. ... 
Deadly nightshade. ... 
Buttercups. ... 
Acorns. ... 
Yew. ... 
Privet. ... 
Rhododendron.