Toxic Parts:
indolizidine alkaloids, selenium, mycotoxins
Flower Color:
  • flower color
  • flower color
  • flower color
  • flower color
meadows, woodlands, xerophyte

Time of Greatest Risk


Geographical Distribution

Locoweeds distribution - United States

Related Species


Astragalus & Oxytropis

Grey Swainsona, Broughton Pea, Swarf Darling Pea, Smooth Darling Pea
8/ 10
Locoweeds are perennial herbaceous plants composed of Astragalus spp. and Oxytropis spp. known for poisoning livestock. These plants contain swainsonine, a toxic indolizidine alkaloid which causes a neurological condition known as 'locoism' in horses. Swainsonine is produced by fungal endophytes that contaminate locoweeds. Locoweeds are a concern for horses living in the rangelands of the western United States, Asia, and South America. Consumption of locoweeds causes horses to display behavioral disorders, gait abnormalities, and neurological symptoms such as ataxia, difficulty standing, standing abnormally, and leg paresis.

Locoweed Toxic Components

All parts of locoweed plants are toxic, resulting in locoweed toxicity if ingested. It remains toxic during all stages of growth, and whether it is fresh or dried. Locoweeds can also accumulate potentially toxic selenium concentrations. Symptoms are usually seen after consumption of large amounts for 2 to 9 weeks. Signs last for several weeks. Young animals are most susceptible. Occasionally horses can recover however it is generally thrifty and will eat locoweed to the exclusion of other forage if returned to infested pasture.

What Locoweeds Look Like

Locoweeds are low or small bushy plants with white, purple, yellow or orange pealike flowers. Leaflets are arranged opposite one other along the stem, with a single leaf extending from the tip of the stem. Seedpods are often inflated.


  • Abnormal Behavior
  • Infertility
  • Abortion
  • Heart Failure
  • Weight Loss
  • Poor Performance
  • Depression
  • Circling
  • Incoordination
  • Staggering Gait
  • Difficult To Handle And Unpredictable


CHEMICAL CONTROL: Locoweed can be controlled by spraying actively growing or budding plants with clopyralid (20-30 gm ae/Ac), picloram (250 gm ai/Ac), and metsulfuron (30 gm ai/Ac). If plants are scattered, treatment of individual plants or patches may be practical.