Stinkweed is a common and problematic weed found throughout Alberta, known for its pungent odor and aggressive growth habits. This invasive plant can quickly overtake gardens, agricultural fields, and natural areas, reducing crop yields and displacing native vegetation. Proper identification and timely control measures are essential for managing stinkweed populations in Alberta’s diverse landscapes.

Stinkweed (Thlaspi arvense), also known as field pennycress, is a winter annual or summer annual weed that belongs to the mustard family (Brassicaceae). It is native to Europe and Asia but has become widely naturalized across North America, including all regions of Alberta. The plant gets its common name from the strong, unpleasant odor released when its leaves or stems are crushed, which is caused by sulfur-containing compounds.

Effective stinkweed management requires understanding its life cycle, growth habits, and the conditions that favor its spread. Alberta’s climate—with cold winters, warm summers, and variable precipitation—creates conditions where stinkweed can thrive if left unchecked. Implementing integrated weed management strategies is essential for controlling this persistent invader.

This comprehensive guide examines the identification, biology, and control methods for stinkweed in Alberta. With the right approach, landowners, farmers, and gardeners can effectively manage this weed and protect their land from its negative impacts.

Stinkweed Identification In Alberta

Physical Characteristics

Stinkweed is a relatively easy weed to identify due to its distinctive features. The plant typically grows 15-60 cm (6-24 inches) tall, though it can reach up to 90 cm (36 inches) in favorable conditions. Key identification features include:

• Leaves: Alternate, oblong to lance-shaped leaves with smooth or slightly toothed margins. The leaves are blue-green in color and have a waxy appearance. The stem leaves clasp the stem with ear-like projections (auricles).
• Stems: Erect, branched stems that are often reddish or purplish at the base. The stems are smooth and hairless.
• Flowers: Small, white, four-petaled flowers arranged in dense clusters at the top of the stems. Flowers appear from early spring through fall, depending on growing conditions.
• Fruit: Flat, round to heart-shaped seed pods called silicles, measuring 1-2 cm in diameter. The pods contain several small, reddish-brown seeds.
• Odor: A strong, unpleasant garlic-like or onion-like odor when the leaves or stems are crushed.
• Root system: A relatively shallow taproot with fibrous lateral roots.

Where Stinkweed Is Found In Alberta

Stinkweed is widespread throughout Alberta and can be found in a variety of habitats, including:

• Agricultural fields: Particularly in cereal crops, oilseed crops, and forage fields.
• Disturbed areas: Roadsides, railway right-of-ways, and construction sites.
• Gardens and lawns: Especially in newly disturbed or poorly maintained areas.
• Natural areas: Grasslands, meadows, and forest edges.
• Waste areas: Dump sites, abandoned lots, and other disturbed locations.

Biology And Life Cycle Of Stinkweed

Understanding the life cycle of stinkweed is essential for developing effective control strategies. Stinkweed can behave as either a winter annual or a summer annual, depending on growing conditions.

Life Cycle Stages

• Seed germination: Seeds can germinate in spring or fall, depending on the ecotype. Germination typically occurs when soil temperatures reach 10-15°C (50-59°F). Seeds can germinate from depths of up to 5 cm (2 inches).
• Seedling stage: Seedlings develop a rosette of leaves close to the ground. This stage is critical for control measures, as young plants are most susceptible to herbicides.
• Vegetative growth: Plants develop stems and leaves, forming a bushy appearance. This stage typically occurs in spring and early summer.
• Flowering: Small white flowers appear in dense clusters at the top of the stems. Flowering can occur from early spring through fall, depending on growing conditions.
• Seed production: After flowering, the plant produces flat, heart-shaped seed pods containing several seeds. A single plant can produce hundreds to thousands of seeds.
• Seed dispersal: The seeds are dispersed when the pods dry and fall to the ground or are carried by wind, water, or human activity.

Seed Viability And Persistence

Stinkweed seeds can remain viable in the soil for 5-10 years or more, creating a persistent seed bank. This long-term viability makes controlling stinkweed a long-term commitment that requires persistence and patience. The seeds are small, reddish-brown, and have a rough surface that allows them to cling to soil, equipment, and clothing.

Why Stinkweed Is A Problem In Alberta

Stinkweed is considered a serious weed in Alberta for several reasons:

• Reduces crop yields: In agricultural fields, stinkweed competes with crops for water, nutrients, and sunlight, reducing yields and quality.
• Taints agricultural products: The pungent odor of stinkweed can taint grain, hay, and other agricultural products, reducing their market value.
• Contaminates livestock forage: When consumed by livestock, stinkweed can taint milk and meat with its unpleasant flavor.
• Displaces native vegetation: In natural areas, stinkweed competes with native plants, reducing biodiversity and altering ecosystem function.
• Allelopathic effects: Stinkweed produces chemicals that can inhibit the growth of other plants, further reducing competition from desirable species.
• Rapid spread: The plant produces large numbers of seeds that are easily dispersed, allowing it to quickly colonize new areas.

Stinkweed Control Methods For Alberta

1. Cultural Control

Cultural control methods aim to create conditions that favor desirable plants over stinkweed. These methods are often the first line of defense and can be highly effective when combined with other control strategies.

• Crop rotation: Rotating crops disrupts stinkweed’s life cycle and prevents the build-up of weed populations. Including competitive crops in the rotation can help suppress weed growth.
• Competitive crops: Planting competitive crops that shade out weeds can reduce stinkweed establishment and growth. Crops with dense canopies are particularly effective.
• Proper fertilization: Maintaining optimal soil fertility through balanced fertilization promotes healthy crop growth, making it more competitive against weeds.
• Good tillage practices: Timely tillage can help control stinkweed by burying seeds or uprooting established plants. However, excessive tillage can bring buried seeds to the surface, promoting germination.
• Maintain ground cover: In lawns and gardens, maintaining a thick, healthy ground cover prevents stinkweed from establishing.

2. Mechanical Control

Mechanical control involves physically removing stinkweed plants to prevent seed production and spread. These methods are most effective when combined with other control strategies.

• Hand pulling: For small infestations, hand pulling is effective if done before flowering and seed production. Pull the plants when the soil is moist to ensure the entire taproot is removed.
• Mowing: Regular mowing can prevent stinkweed from flowering and producing seeds. Mowing should be done at a height that removes flower heads before seed set. Repeated mowing can weaken perennial weeds, but stinkweed is an annual and may require frequent mowing.
• Tillage: Cultivation can uproot and kill stinkweed plants. Tillage is most effective when done in the early seedling stage. However, excessive tillage can promote germination of buried seeds.
• Flame weeding: This method uses heat to kill young seedlings and is effective in the early seedling stage. It is particularly useful for organic growers.

3. Chemical Control

Herbicides are an effective tool for controlling stinkweed in Alberta, particularly when used as part of an integrated weed management program. Several herbicides are registered for stinkweed control in various settings.

• Pre-emergent herbicides: Applied before stinkweed seeds germinate, typically in spring or fall. These herbicides create a barrier in the soil that prevents seedling emergence.
• Post-emergent herbicides: Applied after stinkweed has emerged and is actively growing. These herbicides are absorbed through the leaves and translocated to the roots.
• Selective herbicides: Some herbicides control stinkweed without damaging desirable plants, particularly in lawns and agricultural fields.
• Non-selective herbicides: Products like glyphosate can be used in areas where no plant growth is desired, such as fence lines, sidewalks, and building foundations.

4. Biological Control

Biological control agents, such as insects or pathogens that feed on stinkweed, can help reduce weed populations over time. While biological control is not a quick solution, it can be an effective part of an integrated weed management program.

• Natural predators: Various insects and pathogens feed on stinkweed, including certain beetles, weevils, and fungi. However, specific biological control agents for stinkweed are not yet widely available.
• Grazing management: Proper grazing management can help maintain competitive vegetation that suppresses stinkweed growth.

Recommended Herbicides For Stinkweed In Alberta

Several herbicides are registered for stinkweed control in Alberta. Always check the product label for specific application rates, timing, and safety precautions.

1. 2,4-D (Various Brands)

2,4-D is a selective broadleaf herbicide that is effective on stinkweed in its early growth stages. It is commonly used in lawns, pastures, and agricultural fields. Apply when stinkweed is actively growing in spring or fall.

Pros:

• Selective and safe for most grasses
• Effective on young seedlings
• Cost-effective
• Widely available

Cons:

• Must be applied before flowering
• Less effective on mature plants
• Potential drift to sensitive plants

2. Dicamba (Various Brands)

Dicamba is a selective broadleaf herbicide that provides effective control of stinkweed. It is absorbed through the leaves and translocated to the roots, providing good control even on established plants.

Pros:

• Good systemic action
• Effective on mature plants
• Works well in combination with other herbicides

Cons:

• Potential drift concerns
• Soil residual activity
• Regulated in some areas

3. Glyphosate (Various Brands)

Glyphosate is a non-selective herbicide that kills most plants it contacts. It is effective on stinkweed when applied to actively growing plants. Use in areas where no plant growth is desired, such as fence lines, sidewalks, and building foundations.

Pros:

• Non-selective and effective
• Systemic action
• Fast-acting results
• Breaks down in soil

Cons:

• Kills all plants it contacts
• Requires careful application
• Not for use in lawns

4. Bromoxynil (Various Brands)

Bromoxynil is a contact herbicide that provides effective control of stinkweed in cereal crops. It is most effective on young, actively growing seedlings.

Pros:

• Fast-acting contact action
• Effective on young seedlings
• Safe for cereal crops

Cons:

• Limited residual activity
• Less effective on mature plants
• Requires good coverage

Integrated Weed Management For Stinkweed In Alberta

Integrated weed management (IWM) combines multiple control methods to achieve long-term, sustainable weed control. An IWM approach for stinkweed in Alberta should include:

• Prevention: Preventing stinkweed from establishing is the most effective control strategy. Use clean seed, clean equipment, and monitor for new infestations.
• Cultural control: Implement crop rotation, competitive crops, and proper fertilization to favor desirable plants over stinkweed.
• Mechanical control: Use hand pulling, mowing, and tillage to remove existing plants and prevent seed production.
• Chemical control: Apply herbicides when weeds are actively growing and most susceptible. Use selective herbicides where possible to minimize environmental impact.
• Monitoring: Regularly monitor fields and properties for stinkweed, and take action early to prevent establishment and spread.
• Seed bank management: Prevent seed production to deplete the soil seed bank over time. This may take several years of persistent effort.

Seasonal Management Calendar For Stinkweed In Alberta

Spring (April-May)

• Monitor for stinkweed emergence, especially in disturbed areas.
• Apply pre-emergent herbicides before seed germination.
• Apply post-emergent herbicides to young seedlings before they become established.
• Begin mowing in lawns and pastures to prevent flowering.

Summer (June-August)

• Continue mowing to prevent flowering and seed production.
• Apply post-emergent herbicides to actively growing plants.
• Hand pull or till small infestations before flowering.
• Monitor for new seedlings and take action immediately.

Fall (September-October)

• Apply herbicides to stinkweed before winter dormancy.
• Cultivate soil to disturb and destroy seedlings.
• Prevent seed production by removing plants before seed set.
• Plan spring control measures.

Winter (November-March)

• Monitor for early spring emergence.
• Plan for spring control measures.
• Clean equipment to prevent seed spread.

Frequently Asked Questions About Stinkweed In Alberta

1. What does stinkweed look like?

Stinkweed is a herbaceous plant with alternate, oblong to lance-shaped leaves, small white four-petaled flowers in dense clusters, and flat, round to heart-shaped seed pods. When crushed, it releases a strong, unpleasant garlic-like odor. It typically grows 15-60 cm tall.

2. Is stinkweed poisonous to livestock?

Stinkweed is not generally considered highly toxic to livestock, but it can cause tainting of milk and meat due to its pungent odor and flavor. Large quantities consumed may cause digestive upset. Controlling stinkweed in pastures is important for maintaining forage quality.

3. How does stinkweed spread?

Stinkweed spreads primarily through its numerous seeds, which are produced in abundance and can be dispersed by wind, water, animals, and human activity. The seeds can remain viable in the soil for 5-10 years, making control a long-term effort.

4. What herbicides control stinkweed in Alberta?

Several herbicides are registered for stinkweed control in Alberta, including 2,4-D, dicamba, glyphosate, and bromoxynil. Always check the product label for specific recommendations and safety precautions.

5. Can I pull stinkweed by hand?

Yes, hand pulling is effective for small infestations, especially when the soil is moist. Ensure the entire root system is removed to prevent regrowth. Hand pulling should be done before flowering to prevent seed production.

6. When is the best time to control stinkweed?

The best time to control stinkweed is in the seedling stage in spring or fall when plants are small and actively growing. Controlling before flowering prevents seed production and reduces the soil seed bank.

7. Is stinkweed a regulated weed in Alberta?

While stinkweed is not listed as a regulated weed under the Alberta Weed Control Act, it is considered a significant agricultural weed that requires active management. It is classified as a noxious weed in some other jurisdictions.

Conclusion

Stinkweed is a persistent and problematic weed in Alberta that requires comprehensive management strategies for effective control. The plant’s ability to produce abundant seeds that remain viable for many years makes it a long-term challenge for farmers, gardeners, and land managers. However, with a combination of cultural, mechanical, and chemical control methods, stinkweed populations can be reduced and maintained at manageable levels.

Successful stinkweed management requires understanding the plant’s life cycle, identifying it early, and implementing control measures promptly. Preventing seed production is essential for depleting the soil seed bank and reducing future infestations. An integrated weed management approach that combines multiple control methods provides the most sustainable and effective results.

Alberta’s diverse agricultural and natural landscapes require regionally appropriate management strategies. Consulting with local agricultural extension services, agronomists, and weed specialists can provide specific recommendations for your situation. With persistence and the right approach, stinkweed can be effectively managed, protecting the productivity and ecological health of Alberta’s lands.