Poisonous Plants

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These species are of particular concern to horse owners

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Acer rubrum red maple--no picture

Amsinckia intermedia Fiddleneck

Astragalus and Oxytropis spp. Locoweed --The plant

Astragalus and Oxytropis are leguminous perennials found in large concentrations in western North America. Many species of Astragalus are not poisonous and are good rangeland forage plants. However, within the same species, concentrations of toxicants can vary widely from plant to plant so all locoweeds and milk vetches should be approached with caution and assumed potentially dangerous to livestock. Their leaves are alternate and pinnately compound. Flowers are leguminous and the fruit is a legume pod with kidney shaped seeds. The pod is often conspicuously enlarged causing the seeds to rattle in it when ripe, hence the common names, rattlebox and rattleweed, that are often assigned to it. The keel petal of Oxytropis tends to be long and pointed whereas that of Astragalus tends to be blunter.

Note that these two closely related genuses also carry many of the same toxins

Centaurea solstitialis Yellow Star Thistle

Coronilla varia Crown Vetch

Datura stromonium Jimsonweed --All parts of Jimsonweed are poisonous. Leaves and seeds are the usual source of poisoning, but are rarely eaten do to its strong odor and unpleasant taste. Poisoning can occur when hungry animals are on sparse pasture with Jimsonweed infestation. Most animal poisoning results from feed contamination. Jimsonweed can be harvested with hay or silage, and subsequently poisoning occurs upon feeding the forage. Seeds can contaminate grains and is the most common poisoning which occurs in chickens.

Poisoning is more common in humans than in animals. Children can be attracted by flowers and consume Jimsonweed accidentally. In small quantities, Jimsonweed can have medicinal or haulucinagenic properties, but poisoning readily occurs because of misuse. Ingestion of Jimsonweed caused the mass poisoning of soldiers in Jamestown, Virginia in 1676.

Jimsonweed toxicity is caused by tropane alkaloids. The total alkaloid content in the plant can be as high as 0.7%. The toxic chemicals are atropine, hyoscine (also called scopolamine), and hyoscyamine.

Equisetum arvense and other spp. Horsetail

Fagopyrum Buckwheat

Hypericum perforatum St. John's Wort

Kalmia spp. Mountain Laurel -no picture

Melilotus spp. Sweet Clover

Onoclea sensibis Sensitive Fern

Prunus Wild Cherries: Black Cherry, Bitter Cherry, Choke Cherry, and Pin Cherry

Pteridium aquilinium Bracken Fern

Quercus spp. Oaks

Rheum rhaponticum Rhubarb

Rhododendron spp.--no picture

Ricinus communis Castor Bean --The castor bean plant, Ricinus communis, is a "native of tropical Africa cultivated in several varieties for the oil found in its leaves and for its bold foliage."(Alber and Alber)

The "stalked leaves consist of usually eight radiating, pointed leaflets with slightly serrated edges and prominent central veins. Many varieties are green, but some are reddish brown."(Cooper and Johnson) The flowers are green and inconspicuous, but pink or red in the pigmented varieties. Many stamens are near the base and branching pistils are near the top of the flower. The soft-spined fruits containing attractively mottled seeds are distinctive features of the plant

It is grown as an ornamental in gardens, sometimes as a houseplant, and also grows as a weed.

It is an annual in the south and a perennial in the tropics, and it may reach "15 feet tall outdoors".

It is a woody herb belonging to the family of Euphorbiacea

Aphids, drawn above on a leaf of the castor bean plant, are susceptible to poisoning from ingesting the phloem. The sap-suckers died within 24 hours of feeding.

The European corn borer and the Southern corn rootworm larvae were killed when exposed to feed painted with 2% ricin. Studies like these are undertaken to develop "natural" pesticides.

Castor beans are used as an ingredient in some animal feeds after the oil has been extracted or inactivated by heating for 20 minutes at 140oC. Attempts to use castor beans in feed for livestock involve different methods of inactivating ricin while maintaining nutritional value. Some studies have shown that even afte such heat treatment, toxicity remains. For example, it was lethal to mallard ducks given the feed. "The toxicity of the meal could be due to either a heat stable or growth inhibiting factor or due to minute residues of ricin"(Okoye et al.)

A study with sheepshowed that autoclaved castor-bean-meal can be incorporated to 10% of sheep rations without any ill effect.

Poisoning of livestock usually occurs by accidental incorporation of castor beans in their feed. Horses are particularly vulnerable.

For more detailed information about effects of Ricin on livestock, see... "Poisonous Plants Page, Ricinus Communis, http://res.agr.ca./

Robinia pseudoacacia Black Locust

Senecio spp. Grounsels

Solanum spp. Common Nightshade, Black Nightshade, Horse Nettle, Buffalo Bur, Potato

Sorghum spp. Sorghum or Milo, Sudan Grass, and Johnson Grass

Taxus cuspidata Yew

Trifolium spp. Clover

Festuca arundinacea Tall Fescue --Tall fescue is a hardy, popular, cool season perennial grass that can grow on a variety of soils in a variety of climates. It is grown on an estimated 35 million US acres.

Managing endophyte-infected tall fescue

Converting endophyte-infected fescue to endophyte-free pasture is a challenging task. Changing to endophyte-free fescue may not be the best idea because the endophyte increases the forage's hardiness and promotes growth on marginal soils.

Another option is to diversify a pasture with other forages. This helps reduce fescue toxicity by diluting the concentration of infected fescue.

Nitrogen fertilization appears to increase ergovaline levels in endophyte-infected fescue. Ergovaline levels also increase as plant matures and seed heads form. Keeping livestock off fescue pastures after seed heads appear is advisable, but not always practical. If you cut tall fescue for hay, do it prior to seed head formation, otherwise the hay and remaining stover will be high in ergovaline.

There are three main methods of eliminating endophyte infected fescue. They all involve eliminating the existing fescue, and replanting with endophyte-free fescue seeds .

Prevent seedhead formation in spring by mowing.

In late summer, spray pasture with herbicide, in 2 applications a week apart.

Plant endophyte-free seed

There is about 50% chance of endophyte-infected fescue reappearing.

Intermediate Method:

Spray fescue with herbicide before seeds form.

Plant summer annual.

In fall, spray herbicide on recovering fescue.

Plant endophyte-free seeds.

Better chance of killing infected fescue.

Late summer or ealy fall, spray with herbicide.

Plant winter annual: grass and legume or grass with nitrogen fertilizer.

In spring, spray with fertilizer.

Late summer or fall, sray with herbicide if necessary, and plant endophyte free seeds.

Best chance of killing infected fescue.

Molds of various kinds in various feeds...-no picture

Taken from Cornell University


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Acer rubrum red maple--no picture Fiddleneck Amsinckia intermedia Fiddleneck Locoweed Astragalus and Oxytropis spp. Locoweed --The plant Astragalus and Oxytropis are leguminous perennials found in large concentrations in western North America. Many species of Astragalus are not poisonous and are good rangeland forage plants. However, within the same species, concentrations of toxicants can vary widely from plant to plant so all locoweeds and milk vetches should be approached with caution and assumed potentially dangerous to livestock. Their leaves are alternate and pinnately compound. Flowers are leguminous and the fruit is a legume pod with kidney shaped seeds. The pod is often conspicuously enlarged causing the seeds to rattle in it when ripe, hence the common names, rattlebox and rattleweed, that are often assigned to it. The keel petal of Oxytropis tends to be long and pointed whereas that of Astragalus tends to be blunter. Note that these two closely related genuses also carry many of the same toxins Yellow Star Thistle Centaurea solstitialis Yellow Star Thistle Crown Vetch Coronilla varia Crown Vetch Jimsonweed Datura stromonium Jimsonweed --All parts of Jimsonweed are poisonous. Leaves and seeds are the usual source of poisoning, but are rarely eaten do to its strong odor and unpleasant taste. Poisoning can occur when hungry animals are on sparse pasture with Jimsonweed infestation. Most animal poisoning results from feed contamination. Jimsonweed can be harvested with hay or silage, and subsequently poisoning occurs upon feeding the forage. Seeds can contaminate grains and is the most common poisoning which occurs in chickens. Poisoning is more common in humans than in animals. Children can be attracted by flowers and consume Jimsonweed accidentally. In small quantities, Jimsonweed can have medicinal or haulucinagenic properties, but poisoning readily occurs because of misuse. Ingestion of Jimsonweed caused the mass poisoning of soldiers in Jamestown, Virginia in 1676. Jimsonweed toxicity is caused by tropane alkaloids. The total alkaloid content in the plant can be as high as 0.7%. The toxic chemicals are atropine, hyoscine (also called scopolamine), and hyoscyamine. Back to Top Horsetail Equisetum arvense and other spp. Horsetail Buckwheat Fagopyrum Buckwheat St John's Wort Hypericum perforatum St. John's Wort Kalmia spp. Mountain Laurel -no picture Sweet Clover Melilotus spp. Sweet Clover Sensitive Fern Onoclea sensibis Sensitive Fern Prunus Wild Cherries: Black Cherry, Bitter Cherry, Choke Cherry, and Pin Cherry Bracken Fern Pteridium aquilinium Bracken Fern Oaks Quercus spp. Oaks Rhubarb Rheum rhaponticum Rhubarb Rhododendron spp.--no picture Castor Bean Ricinus communis Castor Bean --The castor bean plant, Ricinus communis, is a "native of tropical Africa cultivated in several varieties for the oil found in its leaves and for its bold foliage."(Alber and Alber) The "stalked leaves consist of usually eight radiating, pointed leaflets with slightly serrated edges and prominent central veins. Many varieties are green, but some are reddish brown."(Cooper and Johnson) The flowers are green and inconspicuous, but pink or red in the pigmented varieties. Many stamens are near the base and branching pistils are near the top of the flower. The soft-spined fruits containing attractively mottled seeds are distinctive features of the plant It is grown as an ornamental in gardens, sometimes as a houseplant, and also grows as a weed. It is an annual in the south and a perennial in the tropics, and it may reach "15 feet tall outdoors". It is a woody herb belonging to the family of Euphorbiacea ANIMALS Aphids, drawn above on a leaf of the castor bean plant, are susceptible to poisoning from ingesting the phloem. The sap-suckers died within 24 hours of feeding. The European corn borer and the Southern corn rootworm larvae were killed when exposed to feed painted with 2% ricin. Studies like these are undertaken to develop "natural" pesticides. Castor beans are used as an ingredient in some animal feeds after the oil has been extracted or inactivated by heating for 20 minutes at 140oC. Attempts to use castor beans in feed for livestock involve different methods of inactivating ricin while maintaining nutritional value. Some studies have shown that even afte such heat treatment, toxicity remains. For example, it was lethal to mallard ducks given the feed. "The toxicity of the meal could be due to either a heat stable or growth inhibiting factor or due to minute residues of ricin"(Okoye et al.) A study with sheepshowed that autoclaved castor-bean-meal can be incorporated to 10% of sheep rations without any ill effect. Poisoning of livestock usually occurs by accidental incorporation of castor beans in their feed. Horses are particularly vulnerable. For more detailed information about effects of Ricin on livestock, see... "Poisonous Plants Page, Ricinus Communis, http://res.agr.ca./ Back to Top Black Locust Robinia pseudoacacia Black Locust Grounsels Senecio spp. Grounsels Solanum spp. Common Nightshade, Black Nightshade, Horse Nettle, Buffalo Bur, Potato Sorghum spp. Sorghum or Milo, Sudan Grass, and Johnson Grass Yew Taxus cuspidata Yew Clover Trifolium spp. Clover Tall Fescue Festuca arundinacea Tall Fescue --Tall fescue is a hardy, popular, cool season perennial grass that can grow on a variety of soils in a variety of climates. It is grown on an estimated 35 million US acres. Managing endophyte-infected tall fescue Converting endophyte-infected fescue to endophyte-free pasture is a challenging task. Changing to endophyte-free fescue may not be the best idea because the endophyte increases the forage's hardiness and promotes growth on marginal soils. Another option is to diversify a pasture with other forages. This helps reduce fescue toxicity by diluting the concentration of infected fescue. Nitrogen fertilization appears to increase ergovaline levels in endophyte-infected fescue. Ergovaline levels also increase as plant matures and seed heads form. Keeping livestock off fescue pastures after seed heads appear is advisable, but not always practical. If you cut tall fescue for hay, do it prior to seed head formation, otherwise the hay and remaining stover will be high in ergovaline. Eradication There are three main methods of eliminating endophyte infected fescue. They all involve eliminating the existing fescue, and replanting with endophyte-free fescue seeds . Fastest Method: Prevent seedhead formation in spring by mowing. In late summer, spray pasture with herbicide, in 2 applications a week apart. Plant endophyte-free seed There is about 50% chance of endophyte-infected fescue reappearing. Intermediate Method: Spray fescue with herbicide before seeds form. Plow pasture. Plant summer annual. In fall, spray herbicide on recovering fescue. Plant endophyte-free seeds. Better chance of killing infected fescue. Long Method: Late summer or ealy fall, spray with herbicide. Plant winter annual: grass and legume or grass with nitrogen fertilizer. In spring, spray with fertilizer. Late summer or fall, sray with herbicide if necessary, and plant endophyte free seeds. Best chance of killing infected fescue. Molds of various kinds in various feeds...-no picture Taken from Cornell University Back to Top