Plants of Texas Rangelands

Virtual Herbarium

Wild Onion

Allium spp.

Liliaceae (Lily family)

Description

There are 14 species and several varieties of wild onions in Texas. These biennial or perennial herbs have strong-scented (odor of garlic/onion), underground bulbs that give rise to long, narrow leaves. The flowers are arranged in a terminal cluster attached to an unbranched stalk arising from the bulb between the leaves. Flower stalks range from 6 to 20 inches or 15 to 51 cm high with blooms of white, yellow, pink, red, or purple. In some species, blooms are replaced by bulblets.

Habitat

Wild Onions are widely distributed across the United States and are found during the spring in every region of Texas and in virtually every soil type.

Toxic Agent

Onions contain N-propyl disulfide, which destroys red blood cells. Cultivated onions contain the same toxin and are often used as livestock feed. Consuming many onions is usually required to cause poisoning: often pastures containing onions are heavily grazed without problems. The amount of toxins in the plants varies based on factors that are not well understood. Cattle and horses are susceptible to onion poisoning, and cats are very sensitive to it. Sheep are more resistant but have been poisoned by onions in some instances.

Signs of Livestock Ingestion

Acute signs usually develop after a long-term intake of the plants and include:
  • Jaundice (yellowish mucous membranes)
  • Depression
  • Anorexia
  • Weakness
  • Dark red or brown urine
Animals showing clinical signs have a strong onion/garlic odor on the breath as well as in the stomach/rumen contents. Sick or dead animals may have an onion odor without onion poisoning. The clinical signs, especially the yellow color and dark urine, must be present to confirm the diagnosis. Diseases such as leptospirosis can also cause these signs.

Management Strategies

Most onion poisoning occurs when animals are fed waste onions. However, some cases occur when cattle or horses are forced to consume large amounts of wild onions. Good range management with adequate forage production will prevent Wild Onion poisoning.

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