Hoary Alyssum

Berteroa incana

Family: Brassicaceae

Weed class: B
Year Listed: 2004
Native to: Europe and Asia
Is this Weed Toxic?:

livestock

Legal listings:

This plant is on the Washington State quarantine list. It is prohibited to transport, buy, sell, offer for sale, or distribute plants or plant parts of quarantined species into or within the state of Washington or to sell, offer for sale, or distribute seed packets of seed, flower seed blends, or wildflower mixes of quarantined species into or within the state of Washington. Please see WAC 16-752 for more information on the quarantine list. For questions about the quarantine list, contact the Washington State Department of Agriculture's Plant Services Program at (360) 902-1874 or email PlantServices@agr.wa.gov.

Why Is It a Noxious Weed?

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.

How would I identify it?

General Description

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.

Flower Description

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.

Leaf description

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.

Stem description

Stems are generally unbranched near base and branched above.

Fruit Seed Description

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.

Where does it grow?

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.

How Does it Reproduce?

Hoary alyssum reproduces by seed.

How Do I Control It?

General Control Strategy

Well-maintained pastures provide suppression of hoary alyssum through competition.

Mechanical Control

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.