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Hoary Alyssum Flower
  • Annual to short-lived perennial

  • Grows to 0.7 meters tall

  • Introduced from Eurasia

Hoary Alyssum Rosette

Hoary alyssum
(Berteroa incana)

Map of RDKB hoary alyssum sites

Quick Identification

  • White flowers with deeply notched petals

  • Entire plant is covered with star shaped hairs

  • Upper leaves are elliptic and clasp stem

  • Oval seedpods are 5-8 mm long, somewhat flattened and held close to the stem

Hoary alyssum spread quickly through fields and along roadsides.  It out competes native species and significantly reduced that capacity of agricultural land for grazing and crops. Contaminated hay spreads seeds, is toxic to horses, and should not be sold.

Small sites can be controlled by hand pulling or digging. Make sure to remove the top inch of the root. this is easiest when soil is moist. Mowing can prevent seed production but does not kill the plant and can lengthen the plant's lifespan. If flowers and seed
are present, bag the plants and dispose of in the landfill.  Selective herbicides are effective.

Has small (5-8 mm in length), white flowers with deeply notched petals that are supported on slender stalks. Sepals are hairy and transient.

Leaves & Stems
The whole plant is covered in star-shaped hairs that are rough to touch, with grey leaves that clasp closely to the stem.

Preferred Habitat
Most common on sandy or gravely soils, hoary alyssum establishes in dry, disturbed habitats, such as roadsides and railway embankments. Hoary alyssum invades dry land, irrigated alfalfa fields, and range lands, tending to increase in forage crops following periods of drought or winter-kill, thus reducing hay quality and value.

Hoary Alyssum Infestation

Reproduction & Dispersal
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.

Slender taproot.

Oval seedpods are chambered and held close to the stem with each chamber containing 5-7 black seeds.

Interesting Facts
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.

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