Identifying Weeds

There are a number of invasive plant species living and growing in the Municipal District of Bonnyville. Through a feature on our Facebook page, we are helping spread the word about these species. This page will be updated a couple of times a month to coincide with the Facebook posts #WeedWednesday.

The information on this page has been provided by the Alberta Invasive Species Council, unless otherwise noted. 

Plant Name

Common Tansy

Common_Tansy

Overview:

Common tansy is a perennial forb that reproduces by both seed and short rhizomes (underground horizontal roots). Introduced from Europe in the 1600’s, its pungently aromatic foliage has been used medicinally, as an insect repellant, and for embalming. 

Common tansy forms dense stands and the plants contain alkaloids that are toxic to both humans and livestock if consumed in large quantities. Cases of livestock poisoning are rare, though, because tansy is unpalatable to grazing animals.

Identification:

Stems: Stems are branched, erect, often purplish-red, and dotted with glands. There are many stems per plant and grow up to 1.5 m tall. 

Leaves: Leaves alternate on the stem and are deeply divided into numerous narrow, individual leaflets with toothed edges.

 Flowers: Flowers are yellow, numerous, and button-like, occurring in dense, flattopped clusters at the tops of the stems. 

Seeds: Seeds are yellowish brown achenes with short, five-toothed crowns.

Prevention:

Because of its long medicinal and horticultural use, Common tansy is still available in plant nurseries and from herbal remedy suppliers. Gardeners should not purchase or grow Common tansy

Control:

Grazing: Common tansy is unpalatable to cattle and horses, but sheep and goats are reported to graze on it.

Cultivation: Since this plant is rhizomatous, flowering stems can re-grow from severed roots, therefore cultivation is not a control option. 

Mechanical: Regular mowing can reduce seed production but must be repeated to eliminate regrowth from rootstock. The most effective control method combines mowing or hand cutting with chemical control and encouraging competition from native vegetation. Repeated stem removal depletes the food energy stored in roots. 


Plant Name

Canada Thistle (Cirsium arvense)

Canada Thistle (Cirsium arvense)

Overview

A colony-forming, aggressive perennial, that spreads primarily by its creeping root system. Despite its name, the plant was introduced from Europe, and is the only thistle, native or introduced, with separate male & female plants. Also called “Creeping Thistle,” the roots spread both horizontally (up to 4.5 metres) and vertically (up to 6 metres) underground. It has been estimated that individual plants live about 2 years, but are continually replaced by new shoots from adventitious buds on its extensive root system. This can result in infestations composed entirely of genetically identical plants of one sex. Dense riparian infestations can impact wildlife by reducing food, and access & nesting cover for waterfowl.

Identification 

Stems: Stems are grooved, upright, hollow and woody, branching near the top, and grow .5 m to 1.5 m tall. 

Leaves: Leaves are lance-shaped, dark green, shiny on the surface and occur alternately, slightly clasping the stem. Lower leaves are largest and decrease in size upward along the stems. Leaf edges can vary from smooth with no spines to irregularly lobed with sharp spines. 

Flowers: Flowers form at the ends of stems in clusters of one to several. The flower head is urn-shaped and the bracts are spineless. The colour of the flowers may vary from plant to plant, being purple, pink or white. 

Seed: Seeds are borne in an achene 2 to 4 mm long which is tufted to aid in wind dispersal. Most seeds germinate within a year, but buried seed can stay dormant for up to 20 years. 

Prevention

The best preventive measure in non-cropland is to maintain healthy plant cover and to reseed disturbed areas with a desirable species as soon as possible. Canada thistle seedlings are very shade intolerant and will not establish under low light conditions. Avoid overgrazing to prevent thistle establishment in pastures/rangeland.

Control

Most of the biomass of Canada thistle plants is below ground; therefore killing the roots is the only effective control method. An integrated management plan that uses a variety control options is the most effective long term strategy for reducing infestations. Grazing: Sheep and goats will readily graze thistle, but not so much in the spiny stage. Occasionally livestock will randomly graze thistle, even when other forage is available, however removal of the stems by grazing only stimulates re-sprouting by the plant. Invasive plants should never be considered as forage.

Cultivation: Cultivation only produces small root pieces that rapidly develop into new plants, and does not reach the deeper roots. 

Mechanical: Repeated mowing through the growing season gradually depletes the food energy stored in the root system. Repeated hand pulling in loose soils can also effectively stress the root system. To succeed, several years of effort must be committed. 

Chemical: 2,4-D, Aminopyralid, Chlorsulfuron, Clopyralid, Dicamba, Glyphosate Hexazinone, Metsulfuronmethyl, MCPA and Picloram are some of the herbicides registered for use on Canada thistle. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information. 

Biological: Several weevils and one fly have been imported to target Canada and other thistle species, but a few are no longer recommended due to impacts on native thistle species


Plant Name

Himalayan balsam (Impatiens glandulifera)

Himalayan Balsam

Overview

Himalayan balsam is a summer annual of riparian areas which reproduces by seed only. 

Native to the western Himalayas, it was introduced to Kew Gardens in the early 1800s. By the 1900s it was already common in southwest Germany and spreading via the Rhine River, and throughout Scandinavian countries by the mid-1900s. Today it is widely known as an invasive alien in temperate areas of Europe, Asia, North America and New Zealand. In Alberta, there are patches along water courses within the cites of Edmonton and Red Deer, as well as Parkland County. 

Seeds germinate in the spring to produce dense, even-aged stands which shade-out competing vegetation. It then exhibits an impressive growth rate for an annual with some plants growing to three metres tall. 

Himalayan balsam has a shallow, fibrous root system but adventitious roots from the lower stems provide some buttressing. However in winter, erosion can occur as a result of balsam’s shallow rooting having replaced the deeper rooted native vegetation. 

Plants flower from July until frost. Flowers are self-compatible but the anthers release their pollen before the stigma is receptive, therefore plant requires pollinators. Himalayan balsam attracts pollinators away from native species with its high nectar content and extended flowering. It is a late season nectar source for butterflies, bees and bumble bees. 

Mature seed capsules explode when disturbed and eject the seeds, hence another common name of Touch-Me-Not plant. Medium sized plants produce on average 700 to 800 seeds which can be flung as far as five metres from the parent plant. Seeds do not float, but can be carried along in water currents and can germinate under water and when fully soaked – seed viability is about two years.

Identification 

Stems: Are smooth, hairless, and usually hollow, tinged red-purple and are easily broken. Stems grow one to three metres tall and there may be some branching. 

Leaves: Are lance shaped or elliptic with pointed tips and rounded bases, and six to 15cm long. The leaves are stalked and have sharply serrated edges. They occur opposite or in whorls of three. Leaf size decreases with height on the stem. 

Flowers: Are large – two and a half to four cm long – in shades of pink through purple, occasionally white. Flowers occur five to 10 together in racemes on long stems borne in the upper leaf axils. Flowers have five petals and are bilaterally symmetrical. The upper petal forms a hood over the reproductive structures (resembling a British policeman’s helmet) and the lower petals form a platform for landing. Seed capsules are one and a half to three and a half cm long and up to one and a half cm wide and contain up to 16 seeds which are four to seven mm long and two to four mm wide. Seeds require cold stratification before germination.

Prevention

Initial spread is mainly from ornamental plantings – do not purchase or grow Himalayan balsam. Seed can be spread by movement of riparian soil and in the sediment from the bottoms of water courses of infested areas. Remedy soil disturbance in suitable habitats. Any control work on infested stands must be done before flowering.

Control

Grazing: Sheep and cattle have been known to graze the plant in Britain without ill effects. Invasive plants should never be considered as forage. 

Cultivation: Likely very effective but cultivation is not practical in riparian habitats. 

Mechanical: Mowing can be very effective but may need to be repeated as cut plants can grow new flowering branches, and would be difficult in riparian areas. Himalayan balsam plants are easily hand pulled due to the shallow root system. Plant debris should be incinerated or bagged and sent to the landfill. 

Chemical: Currently no selective herbicides are registered for use on Himalayan Balsam. The use of herbicides in aquatic environments requires Alberta-specific applicator certification and permits. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman (780-826-3951) or Certified Pesticide Dispenser for more information. 

Biological: CABI began researching natural enemies in 2006 and host specificity testing began 2008.


Plant Name:

White Cockle (Lychnis alba syn. Silene alba S. latifolia)White Cockle 1

Overview:

White cockle was introduced from Eurasia and is often confused with bladder campion (not hairy, not sticky) or night-flowering catchfly (hairy, upper stems sticky), white cockle is not sticky on any part of the plant. It is a short-lived perennial (sometimes biennial) native to Europe. Plants are either male or female, so not all plants produce seed.

Identification:

Stems: Stems are hairy, grow 30 to 120cm tall, and can be erect or spread laterally. There can be several stems per plant – crowded plants branch in the upper stems. Stems are swollen at the nodes.

Leaves: Leaves are opposite, hairy, and lance or slightly oval-shaped with pointed tips. Basal leaves and upper stem leaves are smaller.

Flowers: Flowers are numerous, fragrant and arranged in spreading clusters. The white (or pinkish) flowers have 5 notched petals and only open in the evening. The tubular calyx surrounds the flower’s base. The calyx of the male flower has 10 veins, and the female’s 20 veins are longer, and inflate with ripening. 

Seeds: The calyx matures into a fruit with 10 teeth at the tip containing many tiny, grayish seeds.

Prevention:

White cockle seeds are similar in size to clover and so is often a contaminant of forage seed.

Control:

White cockle can be a serious economic problem as its seeds are difficult to separate from alfalfa, clover and some grass crop seeds – and this invader is an extremely heavy seed producer. This plant emerges early spring, initially forms a taproot, and next spreading lateral roots. 

Grazing: Not grazed. Invasive plants should never be considered as forage. 

Cultivation: Stem and root pieces can sprout to form new plants; therefore cultivation will usually spread an infestation. 

Mechanical: Frequent mowing will reduce seed production. 

Chemical: Mecoprop (in a product mix with 2,4-D and Dicamba) and Tribenuron-methyl (alone or in a product mix with Metsulfuronmethyl and quinchlorac) are registered for use on white cockle. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information. 

Biological: None researched to date.


Plant Name:

Oxeye Daisy (leucanthemum vulgare)Oxeye Daisy 3

Identification:

Stems: Grow up to one metre tall and are smooth, frequently grooved and sometimes branch near the top (although more frequently unbranched).

Leaves: Progressively decrease in size upward on the stem. Basal and lower leaves are lance-shaped with “toothed” margins and petioles that may be as long as the leaves. The upper leaves are alternately arranged, narrow and often clasp the stem with wavy margins. 

Flowers: Are borne singly at the end of stems and can be up to five centimetres in diameter, with yellow centres, and 20 to 30 white petals radiating from the centre. The petals are slightly notched at the tip.

Prevention:

The availability of closely related plants through the nursery and seed trade contradicts the perception of Oxeye as an invasive plant, and subsequent control. Shasta daisy is a cultivar (originated from) of Oxeye sold through nurseries and as seed in wildflower mixes. This fact makes public awareness critical to prevention and control. The two plants can cross breed, resulting in an invasive hybrid that is extremely difficult to distinguish from either parent. Invasive ornamentals can be very difficult to contain and should be avoided. Consumers should carefully read the contents of so-called ‘wildflower’ seed mixes and avoid those containing invasive ornamentals.

Control:

Grazing: Oxeye Daisy is avoided by cattle and therefore capable of dominating pastures and rangeland. Horses, sheep and goats, however, will readily graze oxeye daisy and can be used in companion grazing situations to control oxeye daisy. Switching to higher stock densities and shorter grazing periods does encourage cattle to eat and trample more of the plant. Intensive grazing and trampling slightly reduces the number of seeds produced, and presumably injures younger rootstalks. Trampling also brings dormant seeds to the surface and removes the canopy cover so those seeds will germinate with mid-summer rain showers. In normal years, those seedlings will dry-out and die before becoming established, further reducing the number of seeds in the seed bank. It should be noted, however, that intensive grazing in wet summers may increase the number of successful seedlings. As many as 40% percent of the seeds consumed by cattle may remain viable after passing through the digestive tract, so care should be taken to avoid spreading the seeds when moving stock.

Mechanical: Repeated mowing prevents seed production, but also can stimulate re-sprouting of stems. Hand-pulling or digging before seed production is effective, but it is important to remove as much of the fibrous roots and rhizomes as possible. Ground disturbance while digging should be kept to a minimum. Hand removal will have to be continued for several years because seeds may remain viable in the soil for a long time. Because of its shallow root system, oxeye daisy is easily killed by intensive cultivation. 

Chemical: Aminopyralid alone or in a product mix with Metsulfuron-methyl or 2,4-D is registered for use on oxeye daisy. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information. 

Biological: In 2008 a literature study was conducted to investigate European insect species that feed on oxeye daisy. Studies on ploidy analysis, to be conducted by CABI, and molecular analysis, to be conducted by USDA-ARS, are underway with field collected and commercially available Shasta daisy cultivars to determine the relationship with the target oxeye daisy and assist in host range understanding of potential biocontrol agents. An international consortium, including the Alberta Invasive Species Council, is funding research at CABI1.

Plant Name:

Scentless Chamomile (Tripleurospermum perforatum)

Scentless Chamomile 3Identification: 

Stems: Stems are erect to semi-erect, highly branched, may be reddish in color, and can grow up to 1 m tall. There can be a few to many stems per plant. 

Leaves: Leaves are alternate and very finely divided into short segments (carrot-like) and odorless when crushed. Basal leaves disappear by flowering time. 

Flowers: Flowers are composed of a yellow central disk surrounded by white petals. The flowers are borne singly at the end of stems and have numerous bracts, arranged in overlapping rows. 

Seeds: Seeds are tiny (about 2 mm), ribbed and dark brown. Seeds develop and become viable quickly

Prevention:

Scentless Chamomile does not compete well with vigorous, healthy plant communities. Dispersal by weed seed contamination in crop/grass seed and livestock forage is common. It can be very difficult to eradicate in crop situations.

Control:

Grazing: Scentless chamomile is generally unpalatable to grazers and its seeds can survive digestion. Invasive plants should never be considered as forage. 

Cultivation: Late fall and early spring tillage will control rosettes. Frequent, shallow tillage can help exhaust the seed bank by repeatedly destroying germinating seedlings. Equipment must be cleaned after. 

Mechanical: Mowing can prevent seed production but plants will re-bloom below the cutting height. Hand-pulling can prevent spread into new areas and is effective on small infestations. Pulled plants should be burned or bagged and sent to the landfill. Burning infestations that have finished blooming can prevent seed spread.

Chemical: Aminopyralid (alone or in a product mix with 2,4-D or Metsulfuron-methyl), Chlorsulfuron, Clopyralid (alone or in a product mix with MCPA), Dicamba, Glufosinate ammonium, Hexazinone, Picloram, MCPA (in a product mix with Bromoxynil), Metsulfuron-methyl and Tribenuron-methyl (in a product mix with Thifensulfuron-methyl) are registered for use on scentless chamomile. Always check product labels to ensure the herbicide is registered for use on the target plant in Canada by the Pest Management Regulatory Agency. Always read and follow label directions. Consult your local Agricultural Fieldman or Certified Pesticide Dispenser for more information.

Biological: A seed-head feeding weevil, Omphalapion hookeri, and a gall midge, Rhopalomyia tripleurospermi, have been released in Alberta.