Agronomy • 2023-08-10

Sustainable Pasture Management: Controlling Canada Thistle in Variable Conditions

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Successful, sustainable cattle operations are built on healthy, productive pastureland. When invasive weeds like Canada thistle encroach on your pastures, forage yield and profitability can be significantly reduced.

According to Environment and Climate Change Canada, invasive species that damage the agricultural and forestry industries result in an estimated $7.5 billion of lost revenue annually.¹ The key to keeping Canada thistle from taking over is a commitment to a long-term pasture management strategy that starts with knowing your pasture and its most significant threats.

The root of the issue

A perennial invasive species, Canada thistle is hardy, fast-growing, and aggressively difficult to control. This is due to its extensive root system, which can reach depths of anywhere between six and 18 feet, with lateral growth of up to 20 feet.² Canada thistle reproduces by both seeds and roots, but the primary method of reproduction is via the root system. While cultivation may seem like the solution, Canada thistle can germinate from even small pieces of root, between ⅛ and ¼ inch long.

Preparing for future conditions

One reason why it’s so important to control Canada thistle is its ability to survive harsh conditions like drought. Its extensive root system³ robs moisture and nutrients from the soil, making it much more difficult for more palatable grasses and forage to compete. For this reason, Canada thistle can be especially damaging in drought years, like 2021, when moisture and soil nutrients are already scarce.

With an increasing risk of drought expected for the Southern Prairies in the years ahead⁴, it’s essential to take a proactive and integrated weed management approach that targets Canada thistle at the roots. Using different methods of control will give you the best chance of protecting your pastures today and into the future.

Managing Canada thistle now means more palatable grasses won’t need to compete for moisture and nutrients later, during drought years.

Tool 1: Grazing

Grazing practices can significantly impact the establishment, growth, and spread of Canada thistle. High-intensity-low-frequency (HILF) grazing has been found to significantly decrease the presence of Canada thistle to the point of virtually eliminating it over two to three years.⁵

When HILF grazing is used in the spring, cattle eat the young shoots of Canada thistle as part of their forage supply. However, to avoid breakdown of soil health and forage production, HILF grazing is not recommended to occur year over year on the same pasture at the same time. Instead, be sure to plan a sustainable rotation of pastureland to employ HILF grazing.

Tool 2: Fertilization

Weed control in any crop or pasture begins with healthy competition from other plant species. Enhancing plant competition through fertilization will help to crowd out Canada thistle⁶and other invasive weed species.

Tool 3: Herbicide Application

Broadcast or targeted herbicide applications can help kick-start the process of controlling Canada thistle.⁶ Herbicides like Grazon™ XC, Reclaim™ II and Restore™ II, can be used for both widespread infestations and treatment of smaller, specific areas of pastureland. These herbicides are absorbed by leaves and roots, translocating throughout the plant, providing effective control of Canada thistle. Application should occur once the majority of Canada thistle has emerged, typically throughout July.

Leaving Canada thistle unchecked encourages its growth and virtually guarantees yield and pasture loss.⁶ To manage Canada thistle and ensure the health and sustainability of your pastureland well into the future, look to our Range and Pasture solutions.

Our Range & Pasture portfolio provides producers with sustainable solutions to control invasive weeds, brush and trees in permanent grass pastures and grazed rangeland, allowing for increased grass production and sustainable grazing resources for the future.

To learn more about our portfolio of solutions and additional application timing options for controlling Canada thistle, click here or contact your Corteva Range & Pasture Specialist.