Weed of the Week

Leafy Spurge reproduces primarily by re-sprouting from its extensive, persistent, creeping root system, but also by seed.  It forms dense stands over times and a large plant can produce up to 130,000 seeds. 

All parts of the plant contain a milky-coloured latex that can poison livestock and cause skin irritation on humans. 

This resilient plant grows on a range of soil types and tolerates very dry to very wet climates.

Provincial Designation: Noxious

Learn more from the abinvasives fact sheet.

Even in its native habitats great burdock tends to establish on disturbed ground.  It flowers during the summer and matures early fall. The hooked barbs of mature flowers attach themselves to the clothing and hair/fur of humans and mammals, facilitating seed dispersal.  

Disturbed sites should be reclaimed with desirable vegetation to prevent burdock establishment.

Provincial Designation: Noxious

Learn more from the abinvasives fact sheet.

Field pansy has become a pest of cereal crops and pastures and heavy infestations cause yield losses.   Flowers are self-fertile but also cross pollinated by insects. Flowering and seed production occurs from early spring through to late autumn with an average of 1,500-2,500 seeds per plant. Some seed capsules split explosively upon drying and can propel seeds 2m from parent plant.

Hand pulling would be effective in small infestations before seed production.

Learn more from the abinvasives fact sheet.

Garlic mustard is a shade tolerant plant, but is becoming more common in full sun.

Disturbed soil is the most susceptible to rapid colonization of garlic mustard.   It forms a long, thin, white taproot which has a crook just below ground level. Garlic mustard can self-fertilize or be fertilized by pollinators.

Do not plant garlic mustard in thegarden.

Learn more from the abinvasives fact sheet.

Japanese knotweed grows in coastlands, riparian areas, and salt marshes.  

It is fast growing, long lived, and reproduces primarily via rhizomes. Roots can extend 2-7 m away from the root crown. Fragments of rhizomes can generate new plants.

Learn more from the abinvasives fact sheet.

This is not the chamomile used for tea as it is scent-less.

Scentless chamomile quickly establishes on disturbed sites, farmland and roadsides. A single, robust plant can occupy one full square metre and produce up to one million seeds. 

Learn more from the abinvasives fact sheet.

Yellow flag iris is a Prohibited Noxious weed that grows in wetlands and margins of water bodies.   

It may be confused with cattails or other irises when not in bloom.  Rhizome fragments can drift to new habitats and form new infestations.

Learn more from the abinvasives fact sheet.

Sometimes confused with Garden Phlox (which has 5 petals and opposite leaves), Dame’s rocket has 4 petals and alternate leaves and produces very fragrant flowers.  

It is a prolific seed producer that can quickly take over in moist, shaded woodland edges and grassland areas.

Learn more from the abinvasives fact sheet.

Often perceived to be a ‘pretty’ wildflower, this non-native is an aggressive invader of pastures and natural areas.  It spreads primarily by seed, but also by rhizomes.

Oxeye daisy and Scentless chamomile are often mistaken for each other as the flowers are nearly identical, but the leaves are very different. Both plants are weeds - there are no native white-flowered daisies in Alberta.

Learn more from the abinvasives fact sheet.

Infestations of this Prohibited Noxious Weed can quickly takeover wetlands, thereby out-competing native plant vegetation.  

Seedlings rapidly develop strong taproots from which new shoots arise annually.  Prevention and control of isolated new plants is key, as established infestations are very difficult to eradicate.

Learn more from the abinvasives fact sheet.

Blueweed is also commonly called Viper’s bugloss – the ripe nutlets (seeds) resemble a viper’s head. Historically, this plant had some medicinal uses.  

It reproduces by seed and thrives in  dry, rocky or shallow soils.  Plants develop a long, stout taproot that can grow up to 2 or more feet long. 

Learn more  from the abinvasives fact sheet.

Flowering rush is a Prohibited Noxious weed that can displace native aquatic vegetation and result in reduced water quality which may disrupt valuable fish and wildlife habitat.  

It spreads quickly  by seed or root fragments, so care must be taken when removing existing plants. 

Learn more from the abinvasives fact sheet.

Creeping Bellflower is the bane of gardeners, as it can be an aggressive invader that is extremely difficult to eradicate.  Its creeping roots can travel under fences, lawns, and concrete, making it difficult to control. 

Learn more from the abinvasives fact sheet.

White cockle seeds are difficult to separate from alfalfa, clover and some grass crop seeds.  

Flowers are numerous, fragrant and arranged in spreading clusters. The white (or pinkish) flowers have 5 notched petals and only open in the evening.  This heavy seed producer is an aggressive invader.

Learn more  from the abinvasives fact sheet.

Orange hawkweed will quickly take over grassland by forming dense mats of rosettes.  

This Prohibited Noxious weed is unique among both native and introduced hawkweeds in that its flowers are a fiery orange colour.  All other hawkweed are yellow flowered, and there is one white flowered species. All non-native hawkweeds are noxious weeds.

Learn more from the abinvasives fact sheet.

Himalayan balsam is a Prohibited Noxious weed that is an aggressive invader of wetlands, streams and wet woodlands, where it displaces native vegetation.  

Plants exhibit an impressive growth rate with some plants growing to 3m tall.  Mature seed capsules explode when disturbed and can eject the seeds up to 7 metres.

Learn more from the abinvasives fact sheet.

Field scabious favors grassy areas and can quickly establish along roadsides, open grasslands, and pastures. The flowers very closely resemble those of another ornamental perennial, Scabiosa (butterfly plant, pincushion flower) but each plant belongs to a different genus.

Learn more from the abinvasives fact sheet.

Yellow clematis is a vine species known to smother and out-compete other vegetation.  

It is widely available as both an ornamental plant and seed under a variety of names - Golden Clematis, Golden Tiara, Virgins-Bower - from seed; Radar Love, Helios. C. tibetana is a very similar yellow flowered clematis that is also available and hybridizes with C. tangutica. Do not purchase plants or seeds labeled with any of the names listed above.

Learn more  from the abinvasives fact sheet.

Baby’s breath is used by the flower industry as bouquet filler and sold for dried arrangements.  It is a perennial that reproduces by seed only; a single plant can produce thousands of seeds. 

Dispose of Baby’s breath found in fresh or dried arrangements in landfill bound garbage.

Learn more from the abinvasives fact sheet.

This perennial reproduces by seeds and its extensive, creeping root system.   It has the ability to form  large, dense colonies that readily crowd out native vegetation.

Spurred snapdragon, another common name for this plant, often appears in wildflower seed mixes.

Learn more  from the abinvasives fact sheet.

Black henbane was introduced from the Mediterranean and has been used as a medicinal plant since the Middle Ages.  It was also used in ancient religious rites because of its hallucinogenic properties. It was even used as a flavoring in beer until the Bavarian Purity Law of 1516. 

All parts of the plant are poisonous to humans and animals when ingested.  Black henbane is a prolific seed producer; a single plant can produce as much as half a million seeds in one season, and seeds can remain alive for up to four years.

Learn more  from the abinvasives fact sheet.

Perennial sow thistle has long been an aggressive agricultural weed, but can invade both natural and disturbed sites. 

This weed is prolific around Devon.

Learn more from the abinvasives fact sheet.

This colonizing species can overtake and displace native species in disturbed areas.

Research has shown that the seeds can remain viable in the soil more than 100 years.  

Common mullein is thought to serve as an alternate host for insects that feed on fruit trees.

Learn more from the abinvasives fact sheet.

This highly competitive weed is prolific in and around Devon.   It readily reproduces by seeds or rhizomes.

Dense riparian infestations can impact wildlife by reducing food, and access and nesting cover for waterfowl.

Learn more from the abinvasives fact sheet.

Common tansy is rampant all around the Devon area. 

It will grow in disturbed areas, roadsides and grassland and can form dense stands in these habitats.  The plants contain alkaloids that are toxic to both humans and livestock if consumed in large quantities.

Learn more from the abinvasives fact sheet.