HERBICIDE RESISTANCE BEST MANAGEMENT PRACTICES (BMPs)
1 ROTATE CROPS
- 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.
2 MIX AND ROTATE HERBICIDES
- 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.
1 Herbicide Resistance: Farmer Attitudes, Opinions and Use Patterns, Dow AgroSciences Canada, 2017
2. Please select the BEST description of a true multi-mode of action herbicide:
3 USE RECOMMENDED RATE AND TIMING
- 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).
MORE BMPS TO MANAGE RESISTANCE
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.
Watch the Resistance Management School videos to learn more!
Episode 8: In this episode we’re talking about how herbicide resistant weeds spread across Ontario and the continent.
Episode 7: How do you assess your risk of developing resistant weeds on your farm?
Episode 6: Manitoba farmer Gunther Jochum talks about their wild oat issues in this episode of the Resistance Management School.
Episode 5: Dr. Linda Hall discusses the state of herbicide resistance in Western Canada, and what growers can do about it.
Episode 4: Mike Cowbrough of OMAFRA joins us to discuss testing for herbicide resistance.
Episode 3: Lauren Benoit from the University of Guelph talks about how to manage multiple resistance in water hemp, discovered earlier this year in Ontario. […]
Episode 2: Kelvin Heppner talks to Rob Gulden about seeding rates in this episode of the Resistance Management School.
Episode 1: Dr. Peter Sikkema discusses the status of herbicide-resistant weeds in Ontario and provides growers with some best management practices.