The following table lists common plants known to be toxic when ingested by horses. While this is not a complete list, it contains many plants commonly found in pastures and landscapes in Georgia. Horses generally will not consume the majority of these plants unless deprived of their normal forages.
| Plant Name(s) | Botanical Name/Family | Toxic Plant Parts | Symptoms |
| American Persimmon | Diospyros virginiana, Ebenaceae (Ebony family) | fruit skin, pulp, seeds | ulcers and even rupture of the stomach; severe colic; intestinal obstruction |
| Angel’s Trumpet** | Brugmansia suaveolens (Datura suaveolens), Solanaceae (Nightshade family) | seeds | anorexia, weight loss, thirst, tachycardia, dilated pupils, diarrhea, excessive urination, and death |
| Avocado | Persea americana, Lauraceae (Laurel family) | leaves, bark, seeds, and skin of the fruit | edematous swelling of the lips, mouth, eyelids, head, and neck, which can cause upper respiratory distress; colic |
| Black Locust | Robinia pseudoacacia, Fabaceae (Legume family) | bark, seeds | lectins poisoning; severe gastrointestinal irritation; vomiting and diarrhea; dilated pupils and cardiac arrhythmias |
| Black Nightshade | Solanum nigrum. Solanaceae (Nightshade family) | all parts | taxicardia, decreased salivation and intestinal motility, dilated pupils, and tachycardia; colic, constipation, or hemorrhagic diarrhea |
| Black Walnut | Juglans nigra, Juglandaceae (Walnut family) | unknown- roots, bark, nuts, and pollen of the walnut tree, is possibly involved | horses become poisoned if they are exposed to the wood shavings of black walnuts that are used for bedding. laminitis, edema of the lower legs, colic |
| Bleeding Heart, Dutchman’s Breeches | Dicentra spp., Fumariaceae (Fumatory family) | all parts | projectile vomiting, convulsions, and lateral recumbency |
| Bracken Fern, Brake Fern, Eagle Fern | Pteridium aquilinum, Polypodiacae (Fern family) | fern poisoning in horses is uncommon | depression, muscle tremors, uncoordinated gait, especially of the hind legs and paralysis; colic, constipation, hemoglobinuria, severe anemia, elevated temperature, and rapid heart rate |
| Buckeye, Horse Chestnut | Aesculus spp., Hippocastanaceae (Buckeye family) | young growing sprouts, leaves, immature fruit, and seeds | vomiting and gastroenteritis |
| Castor Bean** | Ricinus communis, Euphorbiaceae (Spurge family) | all parts; seeds most toxic | ricin toxin poisoning; severe gastrointestinal irritation; hemorrhagic diarrhea; dilated pupils and cardiac arrhythmias; death |
| Choke-Cherry, Black Cherry** | Prunus spp., Rosaceae (Rose family) | seeds, leaves, bark, shoots; wilted leaves and new growth most toxic | fatal cyanide poisoning; rapid labored breathing, frothing at the mouth, dilated pupils, ataxia, muscle tremors, convulsions; death |
| Common Boxwood** | Buxus sempervirens, Buxaceae (Boxwood family) | all parts | 1.5 lb of green leaves may be lethal to an adult horse; Severe gastroenteritis, colic, and hemorrhagic diarrhea; death results from respiratory failure |
| Common Cockle Burr | Xanthium strumarium, Asteraceae (Sunflower family) | two-leafed stage of the cockle burr and seeds; burs | liver poisoning; burs cause excessive salivation and mucosa ulcers |
| Corn Cockle | Agrostemma githago, Caryophyllaceae (Pink family) | seeds | gastrointestinal irritation and diarrhea |
| Day-Blooming Jessamine | Cestrum diurnum, Solanaceae (Nightshade family) | all parts | calcification of the elastic tissues of the arteries, tendons, and ligaments |
| Dogbane, Indian Hemp | Apocynum cannabinum, Apocynaceae (Dogbane family) | all parts | Abdominal pain, colic and diarrhea; rapid breathing, cold extremities, and a rapid, weak, and irregular pulse |
| Field Bindweed, Morning Glory | Convolvulus arvensis, Convolvulaceae (Morning glory family) | all parts | colic; intestinal stasis and flatulence; slow heart rate and dilated pupils |
| Flatweed, Cat’s Ears | Hypochaeris radicata, Asteraceae (Sunflower family) | no specific toxin has been identified in flatweed | lameness syndrome characterized by high stepping and hyperflexion of the hind legs; difficulty in stepping backward |
| Hoary Alyssum** | Berteroa incana, Brassicaceae (Mustard family) | all parts; contaminated hay | stiffness, limb swelling, fever, diarrhea, laminitis, intravascular hemolysis, severe hypovolemic shock, and death; abortion or premature parturition |
| Jimson Weed, Thornapple, Stinkweed** | Datura stramonium (D. tatula), Solanaceae (Nightshade family) | seeds | increased heart and respiratory rate, muscle weakness, dilated pupils, colic, and watery diarrhea; death |
| Kentucky Coffee Tree American Coffee Berry** | Gymnocladus dioica, Fabaceae (Legume family) | new sprouts, leaves, and the fruits | gastrointestinal irritation, vomiting, colic, and diarrhea; hypotension, decreased heart and respiratory rates, muscle paralysis, convulsions; death |
| Larkspur, Poison Weed | Delphinium spp., Ranunculaceae (Buttercup family) | all parts | muscle weakness; sudden collapse; rapid exhaustion; muscle twitching, abdominal pain, regurgitation, and constipation. |
| Mayapple, Mandrake | Podophylum peltatum, Berberidaceae (Barberry family) | all parts | colic and diarrhea; excessive salivation |
| Milkweeds** | Asclepias spp., Asclepiadaceae (Milkweed family) | all parts; milky sap or latex | 1.0 kg is lethal for adult horses; death in 8 to 10 hours |
| Monkshood, Aconite** | Aconitum spp., Ranunculaceae (Buttercup family) | all parts | restless, salivate excessively, develop muscle weakness, hypotension; difficulty in breathing; death |
| Mountain Laurel** | Kalmia latifolia, Ericaceae (Heath family) | all parts | green frothy salivation, vomiting, colic, frequent defecation, depression, weakness, ataxia; death |
| Oak | Quercus spp., Fagaceae (Oak family) | leaf and flower buds opening in spring; acorns | excessive thirst; frequent urination; diarrhea; intestinal stasis; teeth grinding and a hunched back |
| Oleander** | Nerium oleander, Apocynaceae (Dogbane family) | all parts; red flower varieties most toxic | severe gastrointestinal and cardiac signs of poisoning; death |
| Peas, Sweet pea | Lathyrus spp., Fabaceae (Legume family) | seeds | osteolathyrism; skeletal deformities and aortic rupture |
| Poison Hemlock, European Hemlock Spotted Hemlock** | Conium maculatum,. Apiaceae (Parsley family) | all parts; seeds highly toxic | salivation, abdominal pain, muscle tremors, and incoordination; difficulty in breathing, dilated pupils, weak pulse, and frequent urination and defecation; death |
| Pokeweed, Pokeberry** | Phytolacca americana, Phytolaccaceae (Pokeweed family) | all parts | oral irritation, excessive salivation, vomiting, colic, bloody diarrhea, depression, prostration, and death |
| Rattlebox** | Crotalaria spp., Fabaceae (Legume family) | all parts; seeds most toxic | liver disease and photosensitization; death |
| Red Maple | Acer rubrum, Aceraceae (Maple family) | wilted or dried leaves, especially in Fall; bark | acute hemolytic anemia; weakness, increased respiratory and heart rates, cyanosis, icterus, and a red-brown coloration of the urine; abortion |
| Rhododendron (Azalea)** | Rhododendron spp., Ericaceae (Heath family) | all parts; nectar | anorexia, excessive salivation, vomiting, colic, and frequent defecation; muscle weakness, bradycardia, cardiac arrhythmia, weakness, paralysis, and coma; death |
| Senecio, Groundsel, tansy ragwort | Senecio spp., Asteraceae (Sunflower family) | all parts | chronic liver disease over a period of 6 or more months. |
| Senna, Coffee Weed, Coffee Senna, Sickle Pod | Cassia occidentalis (Senna occidentalis), Cassia obtusifolia, (Senna obtusifolia), Fabaceae (Legume family) | all parts | afebrile and severely ataxic and may die; acute liver degeneration |
| Sesbania, Coffee Weed, Bladderpod | Sesbania spp. (Daubentonia and Glottidium), Fabaceae (Legume family) | all parts, seeds most toxic | severe hemorrhagic diarrhea; anorexia, abdominal pain, dehydration, and prostration |
| Silver Leaf Nightshade, White Horse Nettle, Tropillo** | Solanum elaeagnifolium, Solanaceae (Nightshade family) | all parts, particularly ripe yellow berries | horses that have recently been treated with the antiparasitic drug ivermectin develop a neurotoxicity; drooling saliva, drooping lips and ears, and head pressing; death |
| Sneezeweed, Bitterweed | Helenium autumnale, Asteraceae (Sunflower family) | all parts | sneezing and vomiting; weight loss, vomiting, and secondary inhalation pneumonia |
| Sudan grass, Johnson grass | Sorghum halepense, Poaceae (Gramineae) (Grass family) | all parts; cyanide poisoning when grass is stressed | posterior ataxia, urinary incontinence, cystitis, and weight loss |
| Tobacco** | Nicotiana spp., Solanaceae (Nightshade family) | leaves | rapid heart rate, salivation, vomiting, colic, and diarrhea; muscle weakness, staggering, collapse of the front legs, and a rapid, weak, and irregular heart rate; respiratory paralysis, blindness, prostration, coma, and death |
| Water Hemlock, Cowbane, Poison Parsnip** | Cicuta maculate, Apiaceae (Parsley family) | all parts, particularly the tuberous roots | 8 oz is lethal for adult horses; muscle tremors and violent convulsions; excessive salivation, vigorous chewing movements, teeth grinding, frequent urination, and defecation are common; death in 2 to 3 hours |
| White Snakeroot** | Eupatorium rugosum, Asteraceae (Sunflower family) | all parts; milk from lactating animals | initially listless, depressed, lethargic, and disinclined to move; choking; patchy sweating; irregular heart rate; death |
| Yew** | Taxus species, Taxaceae (Yew family) | leaves | 8 to 16 oz of yew leaves is lethal for adult horses; muscle trembling, incoordination, nervousness, difficulty in breathing, slow heart rate, vomiting, diarrhea, convulsions, and death |
**Reported to be fatal when ingested in quantity.
References:
Knight, Anthony P. and Walter, Richard G. A Guide to Plant Poisoning of Animals in North America. Jackson, WY: The Innovative Health Science Publisher; 2001.
Plants & Weeds Toxic to Horses. North Carolina Cooperative Extension, NC: Online; 2006. <https://www.ces.ncsu.edu/copubs/ag/livestock/horse/002/>