Hoary alyssum (Berteroa incana) is an annual to short-lived perennial. Considered regionally noxious under the BC Weed Control Act, hoary alyssum is most common on sandy or gravelly soils and establishes on roadsides, railway embankments, and heavily grazed pastures. It is currently found in south-central and southeastern BC including the Okanagan, Cariboo, Boundary, Thompson, and Kootenay areas.
Hoary alyssum has small white flowers with deeply notched petals that are supported on slender stalks. The whole plant is covered in star-shaped hairs that are rough to touch, with grey leaves that clasp closely to the stem. Oval seedpods are chambered and held close to the stem with each chamber containing 5-7 black seeds. Hoary alyssum can grow up to 0.7 metres in height at maturity.
Hoary alyssum spreads rapidly through a long season of seed production. Each plant flowers and produces a large number of seeds between early summer and fall up to frost. Seeds disperse as a contaminant in hay and are spread by vehicles, equipment, footwear, wildlife, and birds. Hoary alyssum invades dry land, irrigated alfalfa fields, and rangelands, tending to increase in forage crops following periods of drought or winterkill, thus reducing hay quality and value.
Warning: Hoary alyssum is toxic to horses, and can cause fever, edema, and laminitis. Sensitivity varies when small or single doses are ingested, and death has only been reported in horses that have consumed hay infested with a large proportion (30-70%) of hoary alyssum.
Refer to Hoary Alyssum T.I.P.S. for information on prevention and control methods.