Hoary Alyssum
Berteroa incana
Washington State Classification
Class B — Control Required (Designated)
It is noted to invade pastures, out-compete beneficial plants and quickly spread through stressed areas.
Required control in Region 1 (all western Washington counties)
Quick Reference
Identification
Growth Habit
Hoary alyssum is an upright annual, biennial or short-lived perennial herb growing about 1 to 3.5 feet tall. Plants are covered in stellate hairs causing it to look silvery-gray in color.
Leaves
Plants have basal and stem leaves. Basal leaves are oblanceolate, 0.75 to 2 inches long by 0.2 to 0.4 inches wide, and have smooth margins. Leaves gradually reduce in size moving up the stem with alternate leaf arrangement.
Flowers
Flowers are in simple or branched clusters (racemes) and bloom from the bottom up. Flower petals white, two times longer than sepals and are deeply cleft. Each flower has 6 stamens.
Fruit & Seeds
Seeds are in somewhat inflated pod-like structures called silicles that are oval shaped and around 0.25 inches long. Seeds are round, brown and have narrowly winged margins.
Impact
It is noted to invade pastures, out-compete beneficial plants and quickly spread through stressed areas. It has been noted for animal poisoning and potentially cause death. Livestock are known to become intoxicated after eating green or dried plants.
Ecology & Spread
Habitat
Hoary alyssum adapted to dry conditions on sandy or gravelly soils. It is found in overgrazed pastures, stressed meadows, roadsides and waste areas. It is increasingly becoming a problem in the Northeast section of the state. Please click here to see a county level distribution map of hoary alyssum in Washington.
Spread Mechanisms
Reproduction
Hoary alyssum reproduces by seed.
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Control Methods
Mechanical
- Small invasions of hoary alyssum can be dug out or hand-pulled. Areas should be surveyed for returning plants and pulled when necessary. Mowing plants can also prevent seed production.