What are some things that are poisonous to horses?

There are many types of plants that are poisionous to horses including rag wort, and fields used for keeping horses should be checked for such plants. I suggest you pick up a book about horsemanship or check the internet for a list of plants and images of them to be sure. Here is a list, but it is by no means complete. * Lantana weed, oak, yew, ragwort, St John's wort * Buttercups (only when fresh - safe when dried) * Mouldy or dirty feed * Black widow Spiders are very poisonous to horses. * Chocolate (is ok in moderation) * Twizzlers, onions, pickles. * Maple leaves in the fall are extremely poisonous to horses. The red leaves on the ground are attractive to some. The tannin in the leaves can cause a horse's kidneys to shut down and most of the time is fatal to the horse. Because maple leaves can be blown into your pasture, be aware of any maple trees in the close surrounding area. * Foxglove flowers Oleander bushes are beautiful and are abundantly planted by cities along developed roads, dividers, and parks. All parts poisonous. Be aware if what these flowering plants look like if you trail ride. too many Apple seeds can be toxis for horses and eating alot of potatoes especially green ones can be fatal and ragwort