Top five tips to manage herbicide-resistant weeds
January 18, 2024
Technical Support Specialist Rob Klewchuk shares his approach to weed resistance management in your cereal field
Herbicide resistance to commonly used chemistries is on the rise, presenting weed management challenges for Prairie farmers.
A recent study out of Agriculture and Agri-food Canada found high resistance in Prairie kochia to Group 2 and 4 herbicides.1
Why is herbicide resistance a problem?
Weeds compete with crops for sunlight, water, space, and nutrients, which can reduce crop yields. With resistance to commonly used herbicides, these weeds are harder to control, leading to more competition and potentially lower yields.
Weeds can also affect the quality of harvested crops by increasing moisture content and introducing seeds or other material that degrade the crops’ value.
What causes herbicide resistance?
Herbicide-resistant weeds are caused when natural genetic changes in a plant allow them to survive herbicide applications that remove a majority of the target weed population.
It is not the herbicide spray causing resistance, but rather the continual use of herbicides with the same control method. Using herbicides with the same control method year over year gives these resistant weeds opportunity to thrive. When individual plants with resistant traits are no longer controlled, they have more space to multiply and gain a foothold in your field.
The challenge, says Syngenta Technical Support Specialist Rob Klewchuk, is that the resistant weeds don’t appear differently from the susceptible weeds when you scout your field.
What are Group 2 and Group 4 herbicides?
Group 2 herbicides, also known as acetolactate synthase (ALS) inhibitors, are widely used for their effectiveness against a broad spectrum of weeds in cereal and pulse crops. However, the extensive use of these herbicides has led to the evolution of resistant weed populations.
In the Canadian Prairies, several weed species, such as kochia, wild mustard, wild oats, and green foxtail, have developed resistance to Group 2 herbicides.
Group 4 herbicides mimic the action of the plant hormone auxin, causing unregulated growth that leads to plant death. These herbicides have been used for many years and are valued for their ability to control broadleaf weeds in cereal crops.
While resistance to Group 4 herbicides is less common than in Group 2 herbicides, it is still a concern, particularly in kochia.
Top five tips for managing resistance
While there’s no silver bullet to resolve resistant weeds in your cereal fields, according to Rob, there are some management best practices he shares with growers.
To manage herbicide resistance, he notes that each field needs to be considered individually.
“Knowing the history of your field through crop plan records, along with monitoring for signs of resistance can help in early detection and management of resistant weed populations and can help you choose your best path forward,” he explains.
Here are Rob’s top five tips on managing resistance:
- Delaying seeding
Allowing weeds to emerge before you apply a herbicide can allow you to reach each leaf for improved coverage and performance results. - Rotate your crops
Rotating crops opens the door for more chemistry options, increasing the likelihood of interrupting the weed life cycle. Simply put, more variability in your crops means each season you can apply a different weed management program to increase your chances of disrupting the weed life cycle. - Choose products that control your target weeds
If you have known resistant weeds in the field, you may have to go with an active ingredient with a more stringent re-cropping label because managing the spread of the resistant weed may be more important than follow crop flexibility. There are not many options for cereal growers to use herbicides with different modes of action, so mixing them can reduce the chance of weeds developing resistance to a single mode of action. - Evaluate your herbicide application method
Reducing the speed of your sprayer, lowering the boom height, and increasing the application water volume used are all methods that can enhance the likelihood of achieving thorough coverage on weeds. - Inspect your fields
Resistance builds over time, so it’s important to inspect your field after each herbicide application to watch for areas where weeds didn’t respond as anticipated. Take note of why that might be – is it resistance or was it an application error, i.e. coverage on the weed. You should add this to your crop plan records so this historical data is available down the road.
Support your resistance management strategy with Syngenta Cereals Solutions®
Talinor™ post-emergent broadleaf herbicide for cereals is the latest addition to the Syngenta portfolio for growers who want to rotate chemistry groups. The unique Group 27 mode of action in bicyclopyrone, along with a Group 6 bromoxynil, help growers proactively guard against weed resistance issues. Talinor offers consistent, fast-acting control of your toughest weeds, including resistant biotypes.
Talinor herbicide gives weed control you can see.
In this photo series taken Nobleford, AB, in June 2023, Talinor herbicide quickly and effectively controlled kochia.
Traxos® herbicide for spring wheat and durum contains two Group 1 active ingredients in pinoxaden and clodinafop-propargyl in a unique formulation of the fastest and safest grass herbicides.
Also for spring wheat and durum growers, Traxos®Two herbicide uses four active ingredients (Groups 1 and 4) for sharper control that is used at a simple, single use rate.
Erebus™ Xtreme herbicide is a convenient pre-mix formulation combining fluroxypyr (Group 4) for broadleaf weed control and pyroxsulam (Group 2). Erebus Xtreme works against wild oats and other grass weeds without compromising resistance management or crop rotation in your wheat and durum and can be tank mixed with other partners to suit your weed spectrum.
In summary
Using herbicides with different modes of action, along with a strategic crop rotation and putting special attention on how you apply herbicides will help western cereal growers manage their herbicide-resistant weed populations.
For more information including articles, resources and videos on resistance management, check out Manage Resistance Now. This is a collaborative effort of industry, academia and government experts, brought together by CropLife Canada, to raise awareness and promote the adoption of strategies to manage weed, insect and disease resistance.
1 https://doi.org/10.1139/cjps-2021-0169
Performance evaluations are based on internal trials, field observations and/or public information. Data from multiple locations and years should be consulted whenever possible. Individual results may vary depending on local growing, soil, and weather conditions.
Always read and follow label directions. Cereals Solutions®, Erebus™, Talinor™, Traxos®, Traxos®Two and the Syngenta logo are trademarks of a Syngenta Group Company.
