Manage Resistance Now


Herbicide resistance costs Canadian growers an estimated $1.1 to $1.5 billion annually due to increased herbicide use and decreased yield and quality. It’s essential to implement weed management programs that provide near-perfect weed control to maximize farm profitability and limit weed seed return to the soil. Ultimately, this will reduce the emergence of herbicide resistant weeds.




It’s critical to adopt best practices to manage resistance and protect crop yield and quality today, ensuring sustainable crop production for the future. Resistance best management practices (BMPs) include a combination of cultural, mechanical, biological, and chemical control measures. Start today, and take it one field at a time.

Rotating crops within a field each growing season is essential to managing herbicide resistance.

  • Crop rotation allows for rotation of herbicide groups, making it more challenging for weeds to develop resistance to repeated use of the same mode of action.
  • Rotate crops with different seeding and harvesting dates. Risk of weed resistance is shown to be the lowest in fields with fall-seeded crops, forage crops, or where three or more crop types (e.g. cereal, oilseed, pulse) are grown over a six-year period.
  • Include crops that compete well with weeds. Plant a range of different crops including a mix of dicots and monocots, winter and spring planted, and annuals and perennials in your rotation.
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Rotate herbicides within and between growing seasons. Use herbicide mixtures and rotate the mixtures for even more impact.

  • Rotate the use of one herbicide group with other herbicide group(s) that control the same weeds in a field. Rotate groups both during a growing season and across years in a field. “Keep the weeds guessing as to what’s coming next,” says Hugh Beckie, former Research Scientist, Agriculture and Agri-Food Canada (AAFC).
  • Herbicide mixtures – the combination of two or more herbicides having different modes of action applied as a single mixture – should be used to delay the onset of resistance to any herbicide. You can mix various combinations of herbicides according to label instructions. Use the recommended label rate of each herbicide for maximum weed kill.
  • Rotate from one herbicide mix to another during a growing season and from one season to the next. It’s easy for weeds to become resistant to simple, predictable weed control. Mixing and rotating makes it unpredictable for weeds and creates diversity for your crop plan.
  • For a mixture to be truly multi-mode of action, both modes of action need to be effective on the same weed species. If you are targeting one species, ensure the herbicides you are using target that weed species.
  • Consider herbicide layering if there are weed escapes after a soil-applied herbicide in the fall or early spring. For example, follow up with a post-emergent application with different modes of action that target the same weed species during the growing season. This can improve weed control and increase your return on investment even in the absence of resistance.
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Using below-label rates of herbicides can contribute to development of resistance. Use the recommended rate, timing and water volume indicated on the label.

  • Using below-label rates of herbicides can contribute to development of resistance. Weeds that survive below-label dosages can develop resistance. Survey your weed populations before spraying so that your weed management is field- and site- specific. Scout fields after herbicide application so that you know how successful you have been in controlling the targeted weeds. This can result in cost savings by reducing herbicide use.
  • For example, in the northern Great Plains, where wild oat is the target weed, site-specific herbicide application on spring cereal crops resulted in higher profits compared to uniform herbicide application.¹
  • When scouting, be aware that isolated weeds listed on the herbicide label that survive application should be dealt with. They may not significantly affect yield at this point, but now is the best time to manage in-field weed escapes.
  • Be mindful of spray techniques.
    • Low travel and wind speeds will allow for more uniform herbicide application
    • Consider boom stability for more uniform droplet deposit
    • Keep in mind that sub lethal doses can occur repeatedly in a field on the periphery or outside of turns and lead to herbicide tolerance

1 Van Wychen LR, Luschei EC, Bussan AJ et Maxwell BD. Accuracy and cost effectiveness of GPS-assisted wild oat mapping in spring cereal crops. WeedSci 50:120–129 (2002).

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Keep accurate records to make informed crop management decisions for each field and even specific areas of a field.

Maximize crop competitiveness by using agronomic practices that promote competition with weeds such as high seeding rates, precision fertilizer placement near or at time of seeding, and optimum seed placement. Factor in crop competitiveness with weeds when making cropping decisions. Growers who rank competitive crops as their top weed management practice have lower incidence of herbicide resistant weeds. Use cover and green manure crops as a weed competitive practice to avoid bare ground.

Use weed sanitation practices like planting weed-free crop seed, cleaning equipment between fields, and applying only composted manure to reduce weed seed additions in the soil seed bank.

Prevent and eliminate weed escapes in field borders and fence rows. These are breeding grounds for weeds, including herbicide resistant weeds. Use spot applications, hand weeding, burning or mowing to eliminate in-field weed escapes and prevent weed seeds from maturing and adding to next season’s seed bank.

Consider strategic tillage since the risk of weeds developing resistance is higher when no-till practices are in place.

Connect with a crop advisor who is familiar with weed biology to help troubleshoot when needed.


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Getting tough on herbicide-resistant wild oats.

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