Hoary Alyssum

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Pest Information
Common Name: Hoary Alyssum
Family Name: Brassicaceae (Mustard Family)
Latin Name: Berteroa incana (L.) DC.
Other Names: Hoary berteroa, Hoary false alyssum, Hoary Alison, Hoary false madwort
Provincial Designation: Prohibited noxious
Seed Act Designation: Primary noxious
Life Cycle: Annual, Perennial
Mode of Spread: Seed

Detailed Information
Provincial Situation:

In Canada, hoary alyssum occurs in all provinces except Nfld. and P.E.I. Alberta had older reports of Hoary Alyssum in Drumheller in 2006. In 2011, reports have come in from the MD of Wainwright, Smoky Lake and Thorhild Counties.


Hoary alyssum has small white flowers with deeply notched petals that are supported on slender stalks. The whole plant is covered in star-shaped hairs that are rough to touch, with grey leaves that clasp closely to the stem. All leaves are alternate (one per node) and entire (without teeth). Basal rosette has oval to lance-shaped leaves that are broadest at the tip. Flowers are clustered near the tips of the stems and branches in simple to compound racemes. Multiple stems are common. Oval seedpods are chambered and held close to the stem with each chamber containing 4-12 black seeds. Seedpods have a seedless beak-like tip extending beyond the valves. The fruit contains 4-12 seeds in 2 rows and is divided by a translucent septum or membranous partition, which remains on the stalk after the pods have slit open and released the seeds. Hoary alyssum can grow up to 0.7 meters in height at maturity and has a slender taproot.

Key Characteristics:

White petals are deeply notched at apex
Hoary appearance of stem, leaves and pods from gray, star shaped pubescence
Leaves entire with smooth leaf edges
Stalk-less, non-clasping leaves with entire margins
Membranous partition in seed pods, obvious after seed has fallen.
4-12 seeds in seed pods

Similar Species:

Alyssum sp. Pale alyssum (Alyssum alyssoides), desert alyssum (Alyssum desertorum), and wall alyssum (Alyssum murale) resemble hoary alyssum, but they are smaller plants with much smaller seed pods (at most 4 mm long) that carry only 1–2 seeds/chamber. Wall and desert alyssum have yellow flowers. http://www.efloras.org/florataxon.aspx?flora_id=1&taxon_id=101238
False flaxes (Camelina sp.) differs by having seed pods 90° to stem, yellow flowers and clasping leaves.  Canada grows camelina for biodiesel production. http://en.wikipedia.org/wiki/Camelina_sativa
Stinkweed (Thlaspi arvense) leaf margins are toothed and seedpod is winged. Alberta grows stinkweed/pennycress for biodiesel production. http://www.anpc.ab.ca/wiki/index.php/Thlaspi_arvense

Where it Grows (Habitat & Ecology):

Hoary alyssum is most commonly found on sandy or gravelly soils and establishes easily on roadsides, railway embankments, and heavily grazed pastures. But can also be found on meadows, pastures, and hayfields. Berteroa incana is considered a xerophytes, which has a low water requirement. Hoary alyssum is well adapted to cold winters and hot, dry summers.

How it Spreads (Mode of Spread):

Hoary alyssum reproduces only from seed.

Reproduction (Dispersal):

Seeds disperse through valves in the seed pods. Germination can occur from early spring to late fall, depending on conditions. Seeds do not appear to travel far from the parent plants by natural means. There is no information on possible dispersal by wind, water, animals, or indirectly in manure or bird droppings.

Economic Importance (Beneficial Aspects):

Berteroa incana has few reported beneficial aspects. Occasionaly, it is used as a bee forage plant in the Caucasus region and is sometimes used in gardens because of the continuously blooming showy flowers.

Toxicity and Other Concerns:

Horses experience depression and a "stocking up," or swelling of the lower legs, 12 to 24 hours following ingestion of hoary alyssum in hay or on pasture. A fever and occasionally short term diarrhea have also been observed. These clinical signs normally subside 2 to 4 days following removal of the alyssum source. In more severe cases, an apparent founder with a stiffness of joints and reluctance of the animal to move has been observed. Recovery of animals with clinical evidence of founder may take several additional days.
In very rare cases, where hoary alyssum comprised extremely high percentages of the hay (30 to 70%), circumstantial evidence exists associating the plant with the death of a few horses. To date, death has not occurred in horses fed hay containing hoary alyssum under experimental conditions.
When mixed with alfalfa in hay, hoary alyssum can remain toxic for up to nine months.


Native to east central Europe. In Canada, Hoary Alyssum was first reported in Ontario in 1893 introduced most likely as a clover and alfalfa seed contaminant. Hoary Alyssum is recognized as an invasive plant in North America since the 1950’s.

Seed Production:

Up to 300 fruits and 2640 seeds per plant are possible under ideal conditions. Hoary alyssum can form a persistent seed bank and seeds can remain dormant but viable for about nine years. Bisexual flowers of hoary alyssum are out crossed and insect-pollinated.


Maintaining healthy stands of vegetation and reseeding after major disturbances are the best ways to prevent establishment.

Cultural Control:

The deep taproot and woody stem of Berteroa incana enable the plant to compete effectively under dry conditions, as well as to resist mechanical means of eradication, such as digging and cutting. The Canadian Botanical Conservation Network suggests the “grub up” method ( use a spade/shovel to loosen soil and dig up the root system) or “shear” treatment (cutting stems close to ground level) for control of B. incana populations. Plant is very difficult to pull up by the roots.


Competing vegetation can greatly reduce seed production. In a Minnesota study, seed production was reduced by 96 percent by having other existing vegetation present.


Hoary alyssum thrives on sites with poor soil fertility.


Tillage is usually not practical option for the habitats occupied by hoary alyssum. But shallow tillage is effective in killing plants provided tap root is severed below the root crown. Tillage would favor the emergence of new plants from seed bank so an integrated approach would be needed to have full control.


Hoary alyssum can produce new shoots from the base of the stem, when cut at above ground level. Mowing alone will not control Hoary alyssum, as neighboring vegetation will also be cut , decreasing the shading ability of neighboring vegetation and is likely to encourage seed spread. Mowing would need to occur on a continuous basis, to be effective in control.


Grazing has not typically been used to control hoary alyssum. Cattle will typically graze more digestible forages and may result in overgrazing which favors the spread of B. incana. Dense hairs on leaves stem and flowers are likely a deterrent to grazing animals and may also repel insects. With that being said, domestic and wild animals will consume B. incana if the plants are sufficiently numerous in their hay or other forage. But hoary alyssum plants are low in crude protein and digestible carbohydrates.


Information is limited on the use of prescribed burning for the control of hoary alyssum.


No bio-control agents, at this time, are available.

Chemical Control:

Before using any products consult product label for specific recommendations and precautionary instructions.

Because hoary alyssum germinates and establishes throughout the growing season repeated applications will be needed. Herbicides for the control of hoary alyssum are likely to remove the legume component of mixed stands.
No incidence of herbicide resistance in hoary alyssum has been reported.

Other Canadian Links:





Herbarium Collections:

None found

Life Cycle:

Hoary alyssum (Berteroa incana) is an annual to short-lived perennial. Seedlings that are established by early July can flower and produce seed by early fall. Seedlings that are established after late July will remain as a rosette and produce seeds the following year.

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Last Modified: January 04, 2012

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