There are many poisonous plants in Wisconsin that could be a potential hazard to horses. These plants may cause symptoms such as:

  • Colic
  • Muscle weakness
  • Incoordination
  • Depression
  • Paralysis
  • Death

Undesired plants can be eliminated in pastures by several methods, however, hand pulling is often most effective. When eliminating these plants, be sure to:

  • Wear gloves
  • Pull plants up by the root (this is easier when the ground is wet)
  • Dispose of the plants far from the horse’s reach
  • Read instructions on any chemical herbicides thoroughly
  • Keep animals off the area as directed after using herbicides

Below is a non-exhaustive list of commonly found plants that can be toxic to horses:

Black Locust

This tree can be found in almost every environment and soil. The bark, leaves, and seeds are all toxic.

  • Symptoms: irregular heart rate, shallow breath, abdominal pain, and death
  • Treatment: supportive care and detoxification

Black Walnut

While the tree itself is not toxic, shavings made from it and should not be used as horse bedding. Wilted or dry leaves can also be toxic for 4 weeks after falling from the tree.

  • Symptoms: laminitis
  • Treatment: treatment for laminitis

Bracken Fern

This plant is also known as Eastern Bracken. It is a perennial fern, and symptoms are slow to develop.

  • Symptoms: depression, tremors, appetite loss, weakness, paralysis, staggering, loss of flesh
  • Treatment: if caught in time, injections of thiamine can help reverse damage


Chokecherry can be extremely lethal in small doses; as little as 2 pounds of leaves can kill an 800 pound animal in 30 minutes.

  • Symptoms: convulsions, rapid breathing, frothing of the mouth, and dilated pupils
  • Treatment: if caught in time, immediate supportive care and IV fluids, with an antidote of sodium nitrate and sodium thiosulfate


Cockleburs are toxic when ingested. As little as 6 lbs. can be lethal to an 800 lbs. horse

  • Symptoms: convulsions, depression, blindness, reluctance to move, hunched back, death
  • Treatment: supportive care

Dried Maple Tree Leaves

While fresh leaves and twigs will not harm horses, wilted or dried leaves can be toxic.

  • Symptoms: weakness, anemia, and increased respiratory rate
  • Treatment: supportive care, IV fluids, blood transfusions and activated charcoal

Eastern Black Nightshade

This plant is also known as Deadly Nightshade, Horse Nettle, or Belladonna. It grows in hedges, pastures and in fence rows. It is a vine with purple flowers and green and red berries.

  • Symptoms: depression, decreased heart and respiratory rate, muscle weakness, watery diarrhea, paralysis of hind legs
  • Treatment: supportive care

Jimson Weed

This plant is also known as Devil’s Trumpet and Thorn Apple. As little as 1 lb. can cause symptoms and more can be fatal.

  • Symptoms: dilated pupils, decreased respiratory rate, and muscle weakness
  • Treatment: if caught in time, activated charcoal, supportive care, and IV fluids

Lawn Clippings

Lawn clippings become toxic as the grass ferments and releases a gas.

  • Symptoms: gas colic
  • Treatment: same as colic treatment

Oak Tree

The acorns, buds, leaves, and blossoms are toxic to horses and livestock.

  • Symptoms: anorexia, colic, bloody diarrhea and edema
  • Treatment: supportive care and IV fluids to flush out kidneys

Ornamental Yew

This plant is also known as Japanese Yew and is commonly used as a landscaping shrub. They are extremely toxic and as little as 6-8 ounces can kill a horse.

  • Symptoms: weakness, labored breathing, collapse, trembling
  • Treatment: if caught in time, treatment can include activated charcoal and assisted respiratory support


This plant is also known as Mountain Laurel. It is extremely toxic to horses and as little as 0.2% of the body weight may be lethal.

  • Symptoms: depression, weakness, impaired vision, difficulty breathing, collapse
  • Treatment: if caught in time, treatment can include activated charcoal

Spotted Poison Hemlock

Also called Water Hemlock Cowbane, this plant is often found near creeks and streams in damp areas. As little as 2 pounds can cause death.

  • Symptoms: incoordination, salivation, and colic
  • Treatment: supportive care

White Snakeroot

This plant is often found along fence rows and woodlines.

  • Symptoms: difficulty swallowing, muscle tremors, and wide stance
  • Treatment: if caught in time, activated charcoal can be used



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