Weed Wednesdays are Back!

Did you know that the Alberta Weed Control Act recognizes two categories of invasive weed species? “Noxious” weeds are those species which property owners are required to control and prevent from spreading.

“Prohibited Noxious” weeds are those species which are required to be destroyed and eradicated from the landscape.

Throughout the summer, the Municipality’s Agriculture and Environmental Services Department will be highlighting an invasive plant species every week during the growing season. Stay tuned to learn more about weeds of concern and how you can do your part to control their spread.

Contact the Agriculture and Environmental Services department at 403-562-8833 for more information on invasive species in the Municipality of Crowsnest Pass.

Brush up on your weed identification skills using this online guide: ID Book 2012 PROHIBITED NOXIOUS (alberta.ca)

Hoary Cress

Lepidium chalepense (Lens-podded)
Provincial Designation: Noxious Weed

Description: Hoary Cress is a creeping perennial with deep rhizomatous roots, that can grow up to 9 meters. It can grow up to 60cm tall and has blue green to gray green colored leaves that are covered with soft white hairs. The leaves are lance to arrowhead shaped and occur in an alternate pattern. It has numerous white flowers with four petals borne on 1cm long stalk. Flowers cluster together at the top of the plant to create a flat-topped appearance. Above ground it reproduces by seed and can produce two crops of seeds per year. Hoary Cress requires disturbance to establish and can be found in meadows, roadside ditches, fields, waterways, cultivated lands and rangelands.

Significant facts: Hoary Cress can be toxic to cattle.

Control method: Encouraging healthy competition by maintaining stands of desirable vegetation. Mowing is effective but needs to be done repeatedly, especially early on before flowering and seed set occurs. There are products registered for use on Hoary Cress. Always read and follow label directions when using herbicides or contact a licensed contractor to perform the application.

Dalmatian Toadflax

Linaria dalmatica
Provincial Designation: Noxious Weed

Description: Dalmatian Toadflax has waxy, pale green to bluish green oval or heart-shaped leaves. It can grow up to 1.4 m tall, and the stalks have bright yellow flowers with a fuzzy orange spot on the lower lip. It has taproots and horizontal roots that can reach depths of 3 m. It grows well in dry sandy or gravely soils.

Significant facts: Dalmatian Toadflax is unpalatable or mildly toxic to livestock. It was introduced from Europe as an ornamental. Each plant can produce up to 500,000 seeds, viable for up to 10 years.

Control method: Remove upper plant prior to seed set to reduce seed production. Repeatedly hand pull young plants.

Dame's Rocket

Hesperis matronalis
Provincial Designation: Noxious

Plant Description: Dame’s rocket was first introduced as an ornamental and is also known as Dames Violet. It is a biennial, and a very prolific seed producer. It produces a rosette in the first year of growth and then a flowering bolt in its second year. Its flowers are very fragrant, with four petals arranged like a cross. Petals are generally purple but can also be white and lavender pink. Its leaves are alternate, and lance shaped with serrated edges. They are dark green in colour and hairy on both sides. Dame’s Rocket is often found growing as an escaped ornamental in moist habitats. It is often found in the moist, humus soils of wooded areas, and forest edges.

Significant Facts: Each plant can produce up to 20,000 seeds, making it a good invader in native plant communities. It can also be a host to crop diseases.

Control Methods: Hand pulling is the most effective method measure as the roots come out easily from moist soils. Plant density may increase the year following control work, but repeated removal will exhaust the seed bank.


Echium vulgare
Provincial designation: Noxious

Description: Blueweed is a short-lived biennial plant. In its first year of growth, it produces a low growing rosette, and a flowering bolt in its second year. It has a black taproot, and its stems can grow up to 90 cm tall. One plant can have one to several stems. Leaves at its base are narrow, lance-shaped, and are stalked. Stem leaves are alternate and become stalkless towards the stop of the plant. Both the stem and leaves are covered with stuff hairs. Flowers are 1-2 cm long and petals are bright blue and funnel shaped. Reproduction occurs through the dispersal of seeds. Blueweed is commonly found in gravelly riparian areas, roadsides, pastures, and meadows.

Significant Facts: Blueweed is toxic to horses and sheep.

Control Method: it is best controlled by hand pulling or digging when soil is moist. Mowing is effective but must be completed repeatedly. There are products registered for use on Blueweed. Always read and follow label directions when using herbicides or contact a licensed contractor to perform the application.  

Common Mullein

Verbascum thapsus
Provincial Designation: Noxious Weed

Description: In its first stage, plants develop a basal rosette of felt-like leaves. It its second stage, a single flowering stem up to 2.5 m tall emerges. Yellow five-lobed flowers attach directly to the stem in a dense, compact spike. It has fuzzy light green leaves thickly covered with felt-like hairs. Common Mullein can overtake and displace native species.

Significant facts: Common Mullein was introduced from Europe as both a medicinal herb and a fish poison. A single plant can develop 100,000-300,000 seeds that can remain viable for more than 100 years.

Control method: Small infestations are easily hand pulled, making sure to remove the entire root.

Orange Hawkweed

Hieracium aurantiacum
Provincial Designation: Prohibited Noxious Weed

Description: Orange Hawkweed is also known as Devil’s Paintbrush. It was introduced from Europe as an ornamental. It has vibrant orange-red flowers, hairy leaves mostly found at the base of the plant, and stems that are mostly leafless with black bristly hairs. The stems can grow 30-90 cm tall with orange-red umbrella-like flowers at the top. It grows at low to mid-elevations in disturbed areas, meadows, roadsides, grasslands, forest openings, and lawns.

Significant facts: Each plant can produce up to 1500 seeds with a 7-year viability. It is highly invasive and spreads quickly. Its above ground runners create a dense mat that impedes other vegetation.

Control method: Hand pulling or digging before flowering can be very effective on small infestations, but it is important to remove as much root as possible and repeat efforts in subsequent years. There are products registered for use on Orange Hawkweed. Always read and follow label directions when using herbicides or contact a licensed contractor to perform the application.

Oxeye Daisy

Leucanthemum vulgare
Provincial Designation: Noxious Weed

Description: Oxeye Daisy is a short-lived perennial that can grow up to 1 meter tall. Its flowers are a single daisy flower head composed of yellow disk flowers in the center, surrounded by white ray flowers. Its stem leaves are arranged in an alternate pattern, are toothed and decrease in size towards the top of the plant. It has short, fibrous creeping roots. It reproduces via seeds, underground creeping roots, and root fragments. Due to this it can quickly form dense populations. Oxeye Daisy can be found in disturbed areas, fields, meadows, roadsides, and forest openings.

Significant facts: Each plant can produce up to 500 seeds which can remain viable for twenty or more years. They can outcompete native vegetation and pasture species.

Control method: Hand pull or dig entire plant before seed set, removing as much of the fibrous roots and rhizomes as possible to prevent regeneration. If flowers have already gone to seed, pick flowerheads bag them and remove. DO NOT mow during or after flowering as it can aid in seed dispersal.

Creeping Bellflower

Campanula rapunculoides
Provincial Designation: Noxious Weed

Description: Creeping Bellflower is a creeping perennial that was introduced to Canada as an ornamental from Europe. Its flowers are purple, bell shaped, and composed of 5 lobes. The flowers are nodding and occur mainly along one side of the stem. Its leaf pattern is alternate, and are heart shaped with jagged edges. Its roots are thick and white, creeping rhizomes.

Significant facts: One plant can produce thousands of seeds per year, with ten-year viability. Due to its rhizome root system, it is a very aggressive plant and is difficult to control.

Control method: hand pulling or cutting and bagging flower spikes pre-bloom can be an option for preventing seed production. Digging out as much of the roots system as possible can be successful, but it will require several years of effort. Mowing will not kill the plant, but will prevent flowering, reducing the seed load. Wildflower seed mixes may contain Creeping Bellflower; do not purchase wildflower mixes that do not list the contents.

Spotted Knapweed

Centaurea stoebe
Provincial Designation: Prohibited Noxious Weed

Description: In its first stage, a basal rosette forms with deeply lobed leaves. Flowering stalks with leaves grow from the rosette in its second stage. Each stalk has a pinkish-purple flower head, and the seed head can persist until the following year. Stems on mature plants have many branches. Spotted Knapweed can grow up to 1.2 m tall.

Significant facts: Each plant can produce up to 2000 seeds which can remain viable for eight or more years. Spotted Knapweed exudes a chemical called catechin into the soil, which prevents the germination of neighbouring plants.

Control method: Hand pull before flowering, being sure to remove as much of the root as possible. If seed heads have formed, bag and remove.  

Black Henbane

Hyoscyamus niger
Provincial Designation: Noxious Weed

Description: Black Henbane is an annual plant that was first introduced from the Mediterranean. It has pale yellow flowers with deep purple veins and throats, that have a strong unpleasant smell. Flowers are bell shaped with five lobes, and there are multiple flowers per stem. Leaves are alternate and large- 15 cm wide and up to 45 cm long. Leaf edges are shallowly lobed and have a terrible smell. Black Henbane can grow up to 1 m tall and has a deep taproot. It reproduces by prolific seed production. It is commonly found in disturbed areas such as roadside ditches, new developments, and field edges. It does not tolerate shade.

Significant Facts: All parts of this plant are poisonous to humans and animals. Despite its toxicity this plant has been used by some since the Middle Ages for its medicinal properties.

Control Methods: Black Henbane is not a strong competitor and can be prevented from establishing by maintaining healthy native vegetation. Hand pulling is effective but be sure to wear thick gloves to prevent rashes. When hand pulling mature plants, they must be bagged to prevent seed dispersal. Mowing is also effective but can be difficult due to the plants thick stem.

Common Burdock

Arctium minus
Provincial Designation: Noxious

Description: Common burdock is a biennial that forms a rosette of leaves in its first year, and a large flowering bolt with many branches the second year. Its stems are erect, branched, and thick with a reddish tinge. Mature plants will grow 1-3m tall. Rosette leaves are large, hairy and heart shaped. Stem leaves are alternate with wavy edges and are wooly underneath. Flowers are purple and have spiny hooked bracts around the florets. Seed production starts in July and continues into fall. A mature plant can produce 6,000 to 16,000 seeds.

Significant facts: Common burdock prefers areas with moist soils-riparian areas- and recent soil disturbance. Its prickly seed heads easily attach to animals and clothing and were the inspiration for the invention of Velcro.

Control methods: Common burdock can be prevented by avoiding soil disturbances, re-seeding bare soil where possible, encouraging desirable vegetation, and inhibiting existing infestations from producing seed. Livestock find burdock palatable, and tilling will kill plants in the rosette stage. Mowing or cutting g can eliminate seed production but should be done after the plant has bolted, but before it flowers. There are products registered for use on common burdock. Always read and follow label directions when using herbicides or contact a licensed contractor to perform the application.