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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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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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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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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It commonly grows along roadsides, waterbodies, fields and pastures, forest openings, disturbed areas, and urban areas. This weed looks similar to scentless chamomile and is often not perceived as an invasive plant because it looks like a wildflower and is sometimes sold in wildflower mixes. Consumers need to fully read the contents of wildflower mixes so they can avoid the spread of invasive ornamentals. (There are no native white-flowered daisies in Alberta.)

Ox-eye daisy is a problem because it can grow in a wide variety of habitats and thrives in low-nutrient soil where other plants are unable to grow. It produces up to 26,000 seeds per plant and the seeds can remain viable in the soil for two to three years. The plant can also reproduce by short, shallow roots (rhizomes). Cattle avoid the plant and so as it spreads, the amount of forage available for grazing decreases. Dense infestations can increase the amount of bare soil in an area as it does not provide good ground cover.

The plant grows up to one metre tall and stems are usually smooth, sometimes branched near the top. The leaves decrease in size as they go up the stem; lower leaves have toothed margins; and upper ones narrow and alternately arranged.

Once this invasive ornamental starts to spread it can be very difficult to contain, so contact your local Agricultural Fieldman if you think you’ve spotted it. For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species Council.

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This noxious weed produces up to 4,000 seeds per plant, and each one is barbed and easily attaches itself to clothing or fur. It also produces toxic alkaloids that cause irreversible liver damage when consumed (typically in hay).

Hound’s tongue is a biennial plant, producing a rosette in year one and a flowering bolt in year two. It has a woody taproot; prefers drier, well-drained sites; and each flower produces four barbed nutlets that can remain on the plant until disturbed and are viable for up to three years.

The name comes from the resemblance of the leaf shape and roughness to a dog’s tongue. It establishes in worked soils but repeated cultivation is helpful control in cropland situations. There are no selective herbicides registered currently and once established, this weed can spread making it very hard to control.

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

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This weed has a taproot that can reach the astonishing depth of four metres, and it can grow as wide as 41 centimetres in circumference. And the multiple tiny white flowers on this noxious weed can produce 10,000 seeds per plant, and allow it to push out native flora and take over the landscape.

During times of drought, such as the one we have just experienced, baby’s breath is able to thrive by accessing water much deeper than most native plants. This can lower the water table to a point that it is inaccessible to native plants desperate for moisture, thereby killing them off and leaving more room for this invasive plant.

Baby’s breath can be identified by it bluish-green colouring and opposite lance-shaped leaves. In the fall, its stalks will turn into a tumbleweed and spread the seeds across the landscape.

Brought over with the settlers in the 1800s, it escaped people’s gardens and has been infesting the landscape ever since. Many infestations can be traced back to graveyards where people left flower bouquets for loved ones. (Any floral arrangements should be disposed of properly in landfill-bound garbage where the seeds will be buried in anaerobic conditions and decompose.)

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

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This invader is a long-lived perennial native in eastern Europe. It produces an abundance of seeds, which have bristles that can easily attach to animal fur. It can be found in flower beds throughout Alberta.

Bighead Knapweed flowers from July to September, and can grow 50 to 170 centimetres tall. It has a large tap root that becomes hardier with age. The leaves are lance shaped and 10 to 30 centimetres long with slightly pointed tips. Leaf margins are smooth, covered with short fine hairs, and dotted with resin glands. Bighead Knapweed is the largest variety in the knapweed family.

Many infestations result from garden or flower bed escapes. That is why it should not be grown as an ornamental.

Bighead Knapweed is listed as a prohibited noxious weed under the Alberta Weed Control Act. Local authorities, such as your local agricultural fieldman, must be notified if it is found.

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

By Tori Cherniawsky, Agricultural Fieldman, Smoky Lake County

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Flowering rush is a perennial of freshwater wetlands that is native to Africa, Asia and Europe and was introduced to North America as an ornamental plant species. It is a prohibited noxious weed, which means it is to be destroyed whenever it is found. It can spread by seed or root fragments so care must be taken with attempts to remove existing plants. It can displace natural vegetation and reduce water quality which may disrupt valuable fish and wildlife habitat.

Flowering rush has triangular stems, sword-shaped leaves, and flowers vary from pink to white in umbrella-shaped clusters.

Control of this weed is extremely difficult. Mechanical control can suppress the plant but will need to be repeated and all parts of the plant must be removed and disposed of in a landfill. Currently no herbicides are registered for use on flowering rush, and applications near water require specific applicator certificates and permits from Alberta Environment and Parks.

For more information on this or any other invasive species contact your Agricultural Fieldman or the Alberta Invasive Species Council.

By Erin McAdam, Supervisor Agricultural operations, Parkland County

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Garlic mustard has severely invaded forest understoreys in other provinces, as it generally prefers shaded areas and rich, moist soils. Disturbed soils are even more prone to rapid infestations. Despite its preference for shade, it is beginning to become more common in areas exposed to full sun.

Garlic mustard ranges from 30 to 90 centimetres tall. The leaves are alternately arranged on the stem, dark green, heart shaped, and become smaller as you move up the stem. When you crush the leaves they have a distinctly garlicky odour. At the top of the stem, you will find white flowers with four petals, arranged in clusters. The rosettes stay green through the winter and stand out against dead foliage in early spring.

Garlic mustard is a prohibited noxious weed. For more information on this or any invasive plant, contact your local Agricultural Fieldman or the Alberta Invasive Species 

–Dawnia Myshak is an agricultural fieldman for the MD of Lesser Slave River.

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