Not only does this pest cause significant yield loss in many crops, but it’s a host for several plant pests that attack economically important crops such as alfalfa, winter wheat and canola — just to name a few.

Fairly widespread from the northeast region of the province all the way to the southern border, perennial sow thistle does best in moist, fertile soils with full sunlight. But it has also adapted well to saline soils. And it is a risky plant in riparian areas as decaying sow thistle emits chemicals which can negatively affect the seed germination of other species.

Perennial sow thistle is a deep-rooted weed that spreads via wind-blown seeds and creeping roots. Yellow, dandelion-esque flower clusters sit at the top of upright stems surrounded with waxy prickled leaves at the base of the plant.

Controlling perennial sow thistle requires a management strategy that reduces weed competition, prevents seed production, and can include a little soil disturbance (which can break up and exhaust fleshy horizontal creeping roots). If this weed becomes established, other control measures are available such as growing competitive crops (such as perennial grasses), using higher seeding rates when planting, mowing to prevent seed production, and hand-pulling seedlings. Chemical controls are also available for perennial sow thistle, however, herbicide resistance is a problem and increased rates may be necessary.

For more information on this or any invasive plant, contact your local agricultural fieldman or the Alberta Invasive Species Council.

Aimee Delaney is a conservation assistant for Red Deer County.

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Jimsonweed is foul smelling and reproduces by seed only. Dense stands will yield an average of 1,300 to 1,500 seeds per plant. It is best eradicated early as it’s a strong competitor, interferes with harvesting equipment, reduces crop yields, and is quite toxic to humans and animals. The concentration of toxins varies greatly from plant to plant, which increases the risk of a fatal overdose.

Identifying this pest is the first step. It has a green to purplish stem along with large, toothed, shrivelled leaves. Its long trumpet-shaped, foul-smelling flowers are enough to give this plant away. In addition to the smelly flowers, the leaves when crushed also give off a vile odour.

Identified control measures include tillage and hand pulling before seed production, and using certain registered chemical controls or fungal pathogens as a biocontrol, but more research is needed. Grazing is not recommended as a control method.

For more information on this or any invasive plant, contact your local agricultural fieldman or the Alberta Invasive Species Council.

Aimee Delaney is a conservation assistant for Red Deer County.

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Once established, Yellow clematis can grow several stems per plant and grow tough and woody with age. Leaves are long, bright green and pointed with a toothed edge. A lemon-yellow nodding flower, hence the name, truly draws the eye to this clematis.

Producing both by seed and stem, the Yellow clematis vine grows rapidly on almost any surface — bare ground, trees and shrubs, up fences, etc. Drought, nutrient-poor soils and cold temperatures don’t seem to hold this invader back.

Unfortunately control can be difficult as cultivation is not known to be successful and grazing controls are not recommended. Herbicides are also not registered for use on Yellow clematis at this time. Mechanical control, or repeated hand pulling prior to seed set seems to be the most effective way to manage this pest.

For more information on this or any invasive plant, contact your local agricultural fieldman or the Alberta Invasive Species Council.

Aimee Delaney is a Conservation assistant for Red Deer County.

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A prohibited noxious weed in Alberta, this pest can be easily identified. Hoary alyssum grows from the base and sends out several stems. Along each stem sits alternate leaves that decrease in size moving up the stem. Sitting atop each stem is a crown of clustered white, four-petal flowers with deep notches for each petal.

Slightly inflated seed pods give this plant away. They are located just below the crown of blooms and have a sharp spike at the tip. Hoary alyssum only reproduces from seed and generally enjoys degraded range and pasture. Seed banks can be viable for several years and when ready, can germinate throughout the growing season.

As anyone who’s battled this weed may know, hoary alyssum is not a great competitor. Controlling this pest can be as simple as maintaining healthy pasture and providing desirable vegetation, which usually is capable of outcompeting this weed.

Livestock will not graze this plant — affected horses exhibit swelling of the legs, depression and diarrhea, which normally subsides a few days after the animal being removed from the infested pasture. There are no selective herbicides registered for use, so other means of control are needed. Hand pulling seems to be most effective on small infestations, but may need to be done repeatedly. Once pulled these weeds should be bagged and disposed of. Burning mature plants will also be effective at destroying the seeds.

For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.

Aimee Delaney is a Conservation assistant for Red Deer County.

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What started as an annual herb in southern Europe has started spreading into Canada (in British Columbia and Ontario). Like most other weeds, this plant prefers areas of disturbed, bare ground and grows as a summer annual in colder climates — which makes it a perfect invader for Alberta.

This low-lying, dense mat-like plant grows very deep taproots. While the above-ground leaves of the plant can be killed by frost, yearly resprouting can occur from these deep roots. Seeds of puncturevine can germinate when spring temperatures and moisture are plentiful. Its greenish-red stems covered in hairs with a yellow, five-petal flower make this weed easy to identify.

The primary control method is early detection and preventing seed production and dissemination. Seeds, which are hard and have two or three sharp spines can puncture feet (humans and livestock) and bicycle tires. They can also bury deep into the soles of footware, only to release later and increase its spread. Seed production is quick, so control efforts are needed through the growing season.

Currently no selective herbicides are registered for puncturevine. As this plant is toxic to animals, this invasive plant should never be considered as forage. Repeated, shallow cultivation before seed production can be the most effective means of control.

For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.

Aimee Delaney is a Conservation assistant for Red Deer County.

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The aggressive perennial Canada thistle is a favourite of disturbed soils of all types. It starts sending shoots from horizontal roots to the surface of soil around mid-April, with flowers to follow in mid-June and continuing throughout the summer.

Easy to distinguish from other weeds, this particular thistle has grooved, upright, hollow and woody stems that branch near the top of the plant. The leaves, generally lobed and spikey, have a tendency to vary in appearance. Usually purple, pink, or white, the flowers on these bothersome plants form at the ends of the stems in clusters of one to several.

It has been estimated individual plants live around two years, but are continually replaced by new shoots on its extensive root system. Maintaining healthy plant cover and reseeding disturbed areas with a desired plant species is the most recommended preventive measure. If however, you find Canada thistle on your land, killing the roots is the only effective control method. Integrated management plans are the most effective long-term strategy for reducing infestations.

For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.

Aimee Delaney is a conservation assistant for Red Deer County.

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Flowers can be a purple- to blue-coloured clustered head, resembling a chive flower. Hairy leaves form a rosette around the base and are deeply lobed. Field scabious can grow up to 1.5 metres tall, but can be very difficult to see from a distance, as it is so thin and spindly. This plant prefers nutrient-rich, moderately dry soils and develops a deep taproot that will compete with native grasses for resources.

The goal for control of this weed is to stop seed production. However, be careful when hand pulling because this plant will cause skin irritation and itching, so it is best to wear long sleeves and gloves. Field scabious is listed as noxious under the Alberta Weed Control Act and therefore must be controlled, meaning its growth or spread must be prevented.

For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.

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Absinthe wormwood also has a very strong and distinct odour which is very similar to sage. It is one of the major ingredients in the namesake alcoholic beverage popular in the bohemian culture of 19th- and early-20th-century France.

The compounds responsible for this odour cause animals to avoid grazing it and can even give cow’s milk an ‘off-taste.’ It is most commonly found in dry, open waste areas, as well as overgrazed pastures and roadsides. Since it mainly invades overgrazed pastures and other disturbed areas, the best method of control is through prevention by means of proper grazing management.

Once established, there are still some control options. Tillage can be effective in cropped areas. Mowing can prevent seed production but will need to be repeated several times and will not reduce an infestation. Hand pulling is not recommended because of its deep taproot. Several herbicide options are available.

For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.

– Submitted by Jordon Smith, agricultural technician, Red Deer county

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It was originally brought to North America from Eurasia as an ornamental, but soon spread throughout the continent. High seed production and excellent tolerance to Canada’s climate allow this tree to outcompete many native species.

Common buckthorn is a deciduous shrub or tree, growing to seven metres or more. Branches are usually tipped with a spine, and scratching away the outer bark will reveal bright-orange inner bark. The best time to scout for this tree is at the very beginning and end of the growing season, as it is one of the first trees to grow and shed its leaves.

Control of this species usually involves a combination of mechanical, cultural, and chemical methods. Whole tree removal, berry removal, chemical herbicides, and mulching combined with revegetation are some options that should be used together.

The earlier this invasive prohibited noxious weed is found, the less costly and time consuming control will be. For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.

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Woolly burdock can only reproduce by seed, but is self-fertile due to the flowers being hermaphroditic (having both male and female organs). A mature plant can produce anywhere from 6,000 to 16,000 seeds.

An easy way to identify this weed is by looking at its flowers, which are covered with spiny barbs and cobweb-like hairs. The flowers, which branch off and form round clusters, can range from rose, purple, to white in colour. The stems (light green, grooved with a purplish tinge) and leaves (heart shaped and alternating) also contain cobwebby or woolly-like hairs.

Woolly burdock is similar to great burdock (which has larger flower heads) and lesser burdock (which has flower heads with sessile stems that don’t branch off as woolly burdock flowers do).

Because its flower heads are barbed, livestock won’t graze on woolly burdock. But if the barbs become entangled in an animal’s hair it will cause matting, and sometimes injury. By hitching a ride on animal hair or people’s clothing, weed seeds are easily dispersed.

Control of woolly burdock is achieved by digging up plants or cutting them prior to flowering. No current herbicides are registered for use on this weed.

For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.

By Shaylin Exshaw, senior weed and pest inspector, Yellowhead County

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