06/30/2026
๐ฑ ๐๐จ๐๐ซ๐ฒ ๐๐ฅ๐ฒ๐ฌ๐ฌ๐ฎ๐ฆ: ๐ ๐๐จ๐ฑ๐ข๐ ๐๐๐๐ ๐๐ฏ๐๐ซ๐ฒ ๐๐จ๐ซ๐ฌ๐ ๐๐ฐ๐ง๐๐ซ ๐๐ก๐จ๐ฎ๐ฅ๐ ๐๐ง๐จ๐ฐ
Time to kick off a new educational series on common plants and w**ds found in horse pastures and hay!
Some are simply a nuisance, while others can have serious consequences for your horse's health. First up is one of the most common toxic w**ds horse owners should recognize โ Hoary Alyssum.
๐ฟ ๐๐ก๐๐ญ ๐ข๐ฌ ๐ก๐จ๐๐ซ๐ฒ ๐๐ฅ๐ฒ๐ฌ๐ฌ๐ฎ๐ฆ?
Hoary alyssum (Berteroa incana) is an herbaceous forb that belongs to the broadleaf mustard family. It grows up to two feet tall and has small white flowers, each with four deeply notched petals.
๐ ๐๐ก๐๐ซ๐ ๐ข๐ฌ ๐ข๐ญ ๐๐จ๐ฎ๐ง๐?
Originally native to Eurasia, spanning Eastern and Central Europe as well as Western Asia, hoary alyssum is now widespread throughout North America. It is primarily found in the Northern and Western United States as well as southern and central Canada.
It was accidentally introduced as a contaminant in clover and alfalfa seed in the late 19th and early 20th centuries and was first documented in Wallbridge, Ontario, in 1893. Since then, its rapid spread has been driven by the movement of contaminated hay, gravel, soil, and farm equipment.
๐ฑ ๐๐ก๐๐ซ๐ ๐๐จ๐๐ฌ ๐ข๐ญ ๐ญ๐ก๐ซ๐ข๐ฏ๐?
Hoary alyssum is most abundant in disturbed areas. These disturbances may result from overgrazing, animal traffic, tilling, plowing, mowing natural borders, or removing topsoil. Additionally, hoary alyssum is common in sandy soils and can take advantage of poor, drought-stressed conditions where it outcompetes desirable forage species.
โ ๏ธ ๐๐ก๐๐ง ๐๐จ๐๐ฌ ๐ข๐ญ ๐ฉ๐จ๐ฌ๐ ๐๐ง ๐ข๐ฌ๐ฌ๐ฎ๐ ๐ญ๐จ ๐ก๐จ๐ซ๐ฌ๐๐ฌ?
Both fresh and dried hoary alyssum are toxic to horses, meaning it can be dangerous whether it is growing in pasture or baled in hay.
Typically, hay or pasture containing 30% or more hoary alyssum by weight can be dangerous for horses. However, some horses develop signs of toxicity with as little as 10 to 20% of their diet containing the w**d.
Due to its bitter taste, horses often avoid hoary alyssum on pasture unless other forage is limited. The greater risk occurs when it is incorporated into hay, where horses cannot easily sort it out.
Notably, while hoary alyssum is toxic to horses, ponies, and donkeys, other livestock such as cattle, sheep, and goats can safely consume the plant.
๐ฉบ ๐๐ก๐๐ญ ๐๐ฅ๐ข๐ง๐ข๐๐๐ฅ ๐ฌ๐ข๐ ๐ง๐ฌ ๐๐ซ๐ ๐จ๐๐ฌ๐๐ซ๐ฏ๐๐?
Currently, the toxins in hoary alyssum have yet to be identified, but they disrupt the circulatory and inflammatory systems within the horse.
If a horse consumes a toxic amount of hoary alyssum, clinical signs typically appear within 12 to 24 hours. The main signs include swelling of the limbs, lameness, laminitis, and colic.
๐ ๐๐จ๐ฐ ๐ข๐ฌ ๐ข๐ญ ๐ญ๐ซ๐๐๐ญ๐๐?
The first steps are to immediately remove the source containing hoary alyssum and contact your veterinarian to assess the severity of the condition. Treatment often includes IV fluids, electrolyte therapy, and management of laminitis if it develops.
With proper supportive care, many horses show improvement within 2 to 4 days, although it can take months for some horses to return to full performance.
๐ ๐๐จ๐ฐ ๐๐จ ๐ฒ๐จ๐ฎ ๐ ๐๐ญ ๐ซ๐ข๐ ๐จ๐ ๐ข๐ญ?
Hoary alyssum is primarily an annual, meaning it completes its life cycle in a single growing season and reproduces entirely by seed. Preventing seed production is therefore one of the most effective ways to reduce future infestations.
Because it has a taproot, hand-pulling or mechanical removal is the most effective control method for small infestations. If the w**d is widespread, mowing before seedheads develop can help reduce future spread, although it will not eliminate existing plants. Avoid mowing once seeds have formed, as this can spread the seeds even farther.
When infestations are severe, cultural practices such as prescribed burning and reseeding with desirable forage species may be beneficial. As a last resort, the herbicide 2,4-D can provide effective control when applied before the plants flower.
โ
๐๐จ๐ง๐๐ฅ๐ฎ๐ฌ๐ข๐จ๐ง
The best way to protect your horse is to recognize toxic plants before they ever make it into the pasture or hay bale. Regular pasture inspections, purchasing quality hay, and learning to identify common w**ds can go a long way toward preventing a potentially serious poisoning event.
Have you ever encountered hoary alyssum in your pasture or hay?
What w**ds or toxic plants would you like me to cover next?
Cheers,
Dr. DeBoer
