Vectors of Spread:
- Hoary Berteroa
- Hoary False Alyssum
General: An annual, biennial or short-lived perennial.
Flowers: Small, white flowers 5 – 8 mm long with deeply notched petals. The sepals are hairy and transient.
Stems: Are erect, thin and grow from the base of the plant and branch near the top. Each plant has single or multiple stems, which can be 0.3 – 1.1 m tall and are covered in star-shaped white hairs.
Leaves: Upper leaves are elliptical, face upward, lack stalks and clasp the stem. Lower leaves have long, slender stalks and are 3 – 5 cm long. All the leaves are covered in rough, star-shaped hairs.
Seeds: Black, 2 – 3 mm long and are aligned in chambers in the seed pod.
Fruit: Flattened, oval-shaped seed pods that are 5 – 6 mm long, are held close to the stem and covered in white, star-shaped hairs. Each pod contains 4 – 12 seeds.
Roots: Slender taproot.
Pale Alyssum (Alyssum alyssoides) is an annual or biennial herb with multiple, erect stems that branch near the base of the plant. The leaves are 5 – 25 mm long, narrow and covered in grey star-shaped hairs. Flowers are white or cream-coloured, are 3 – 4 mm long and covered in star-like hairs. Pale Alyssum can be found growing along roadsides and waste areas.
Desert Alyssum/ Desert Madwort (Alyssum desertorum) a herbacious annual that is native to Africa, Asia and Europe. It has multiple, erect stems that branch near the base of the plant and can grow to 30 cm tall. Leaves are linear or broadest at the tip. Flowers form from the bottom of the plant as the inflorescent grows and have four pale yellow or white-ish petals.
Wall Alyssum (Alyssum murale) is a perennial herb that has multiple, erect stems that branch near the base of the plant and can be between 25- 70 cm tall. The basal leaves are egg shaped, and stem leaves are 10- 20 mm long, 3-6 mm wide, lanceolate and covered in grey, star-like hairs. Flowers are less than 2- 3.5 mm long, with narrow yellow petals. It grows in dry, disturbed areas and waste places.
False Flax (Camelina sativa) an annual plant that can grow 30- 90 cm tall. Stems are branched, become woody at maturity and are generally smooth. Leaves are arrow-shaped and 2.5- 8.5 cm long. Flowers are small and pale yellow or a greenish-yellow with 4 petals.
Habitat and Origin
Hoary Alyssum is native to Eastern and Central Europe and is believed to have been brought to North America as a seed contaminant. It was first discovered in Ontario but wasn’t classified as an invasive species until the 1950’s.
Hoary Alyssum is well adapted to dry, sandy, gravelly, nutrient poor soils. It can be found growing in idle areas, over-grazed or stressed pastures or meadows, hayfields, roadsides and railways. It can withstand cold winters and dry, hot summers.
Propagation & Vectors of Spread
Hoary Alyssum reproduces solely by seed. Germination occurs from early spring through to fall, with each plant producing up to 2,600 seeds under ideal conditions. Seeds can remain viable in the soil for up to nine years which leads to the rapid formation of a seed bank.
Hoary Alyssum seeds are dispersed through valves in the seed pods. The seeds are spread by vehicles, equipment, footwear, wildlife and birds; they are also a hay contaminant.
Ecological and Economic Impacts
- Out-competes native plants and can displace weak native plant communities.
- Decreases forage value as mature plants are low in crude proteins and digestible carbohydrates.
- Toxic to horses if eaten which can result in illness and occasionally death.
What Can I Do?
Hoary Alyssum is currently found throughout the Sea to Sky Corridor, so the best approach to controlling its spread is by PREVENTION.
Learn to identify Hoary Alyssum: use the images presented in this profile page to learn how to identify Hoary Alyssum.
What to do if you spot it: You can report any Hoary Alyssum sightings by clicking here.
- Regularly monitor properties for weed infestations.
- Ensure soil and gravel are uncontaminated before transport.
- Check wildflower mixes to ensure that they do not contain Hoary Alyssum.
- Ensure that plants are disposed of in a garbage bag if found in floral arrangements to prevent seeds from spreading.
- Unload, park or store equipment or vehicles in infested areas; remove plant material from any equipment, vehicles or clothing used in such areas and wash equipment and vehicles at designated cleaning sites before leaving infested areas.
- Plant Hoary Alyssum in a garden, no matter how well-contained its enclosure may seem.
- Move soil that has been contaminated with Hoary Alyssum.
- Do not compost Hoary Alyssum.
Hand-pulling small infestations and planting native, competitive plants will help to reduce the growth of Hoary Alyssum plants. Mowing or grading as early as possible in the season and repeating regularly will also help to control infestations.
Combining 2,4-D and dicamba has been proven most effective. Additionally, 2,4-D, dicamba and metsulfron methyl can be used effectively on their own. Glyphosate can also be used, however it will kill off surrounding vegetation. Spring applications when plants are actively growing and prior to bolting will be most effective. Because Hoary Alyssum germinates and establishes throughout the growing season, repeated applications will be needed to target plants regenerating from the seed bank.
We recommend that any herbicide application is carried out by a person holding a valid BC Pesticide Applicator Certificate. Before selecting and applying herbicides, you must review and follow herbicide labels and application rates; municipal, regional, provincial and federal laws and regulations; species-specific treatment recommendations, and site-specific goals and objectives.
There are currently no forms of biological control available for Hoary Alyssum.
Alberta Agriculture and Forestry, Hoary Alyssum, http://www.agric.gov.ab.ca/app107/loadPest?action=display&id=244
eFlora, Alyssum Murale, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Alyssum+murale
eFlora, Pale Alyssum, http://linnet.geog.ubc.ca/Atlas/Atlas.aspx?sciname=Alyssum%20alyssoides
Invasive Species Council of British Columbia, Hoary Alyssum,https://bcinvasives.ca/invasives/hoary-alyssum/
Invasive Species Council of British Columbia, Hoary Alyssum TIPS Factsheet, https://bcinvasives.ca/wp-content/uploads/2021/01/Hoary_Alyssum_Factsheet_20_02_2019.pdf
Ministry of Transportation, Hoary Alyssum (P.33), https://prrd.bc.ca/wp-content/uploads/2014/12/ManagingInvasivePlants.pdf
United States Department of Agriculture Natural Resources Conservation Service, Plant Guide: Camelina sativa, https://plants.usda.gov/plantguide/pdf/pg_casa2.pdf
United States Department of Agriculture Natural Resources Conservation Service, Plant Guide: Hoary Alyssum, https://plants.usda.gov/factsheet/pdf/fs_bein2.pdf