Hoary Alyssum

Identification & Biology
Latin Name : Berteroa incana
Category : Terrestrial Plants
Description :
  • Annual to short lived perennial
  • White flowers 4-6 mm long with 4 deeply notched petals
  • Slender taproot
  • Erect and branched stems covered with star-shaped hairs (0.3-1.1 m tall)
  • All leaves are greenish-grey and lower stems purple
  • Flattened oval seed pods are 5-8 mm long, have star-shaped hairs, and are held close to the stem

Hoary alyssum plants can vary in form considerably depending on site-specific conditions such as soil type, nutrient availability, moisture, and competition. These variables may cause them to be simple, slender and unbranched, to partially branched, or even fully branched and rounded. Hoary alyssum is commonly referred to as a biennial, but can also behave as an annual or perennial at times. It reproduces only by seed. The plant emerges as a rosette in early spring and then bolts and grows a cluster of white flowers. From late spring flowers and seeds continue to be produced until the first frost. When acting as a perennial, it over-winters as a rosette and emerges again in the spring.

Habitat

In British Columbia, hoary alyssum occurs in the Thompson, Okanagan and Kootenay regions. It prefers dry sandy or gravely soils and establishes well in dry, disturbed habitat such as pastures, hayfields, roadsides, rangelands and embankments.

Impact & Risks

Hoary alyssum can be very troublesome to ranchers, as horses have been known to become intoxicated after eating green or dried hoary alyssum plants. Some symptoms associated with severe intoxication include stiffness, fever, diarrhea, intravascular hemolysis, and hypovolemic shock. Death has only been recorded in horses eating hay infested with 30-70% hoary alyssum. Ruminants (cattle, sheep, goats, and llamas) are not known to have adverse reactions to it.

Prevention & Mitigation

The most effective way to ensure that your lands do not become infested with hoary alyssum is by prevention. Here are some recommendations to prevent hoary alyssum from invading your property:

  • Maintain your crops and natural lands in a healthy, vigorous condition to ensure a competitive plant community; competitive perennial grasses and forbs utilize water and nutrients that would otherwise be readily available to hoary alyssum.
  • Regularly patrol your property for hoary alyssum plants and immediately control or remove infestations before seed set. Do not leave plants to compost as they may still produce viable seed.
  • Cooperate with adjacent landowners and encourage them to prevent hoary alyssum spread.
  • Immediately re-vegetate disturbed, bare soils with a suitable seed mixture that provides dense, early colonization to prevent weed invasion.
  • Do not move contaminated soils to a new area.
Treatment & Disposal

Small populations of hoary alyssum can be successfully controlled by diligent hand-pulling or hoeing in the spring during seedpod development to prevent seed production. Mowing is ineffective on hoary alyssum. Continually re-visit sites annually and remove new plants, before they go to seed. Re-vegetate managed areas with competitive, desirable plants to compete against re-invasion Chemical control is also an option. Before applying herbicides, read the label for full use and precautionary instructions. Consult the most recent edition of the Alberta Agriculture and Forestry Crop Production Guide for the selection and application of chemicals to protect your crop:  There are no biological controls for hoary alyssum available at this time.

Okanagan Distribution

Priority Level Definitions

Watch For - Poses a significant threat (very high risk) and does NOT presently occur in the region OR is relatively new to the region and is very limited in extent.
High - High risk/impact; limited population with significant potential to spread in the region.
Medium - Medium risk/impact; limited distribution – broader population distribution with potential to spread further in a region.
Low - Low risk/impact; may be widespread or not, may be of concern in specific situations with certain high values – e.g. specific agriculture crops. Some species may be treated primarily with biological control agents.