As herbicide resistance continues to grow, Western Canadian growers are looking for ways to protect the weed control options that still work.
One way is to diversify how problem weeds are controlled so that the same herbicide group or application window isn’t repeatedly asked to do all the work. This can include layering multiple effective modes of action across different application timings.
A program that uses different products is not necessarily diverse. Before you can add a meaningful layer of control, you need to understand which active ingredients and herbicide groups are doing the work.
Switching products doesn’t necessarily add diversity
Remember, different products and different active ingredients can belong to the same herbicide group. As Nufarm Technical Services Manager Tyler Gullen puts it, “switching products doesn’t necessarily mean you’re switching up groups.”
Premixes also need a closer look. A product may contain two or more herbicide groups, but each group must be effective against the target weeds to add a meaningful layer of control. If only one component controls the weeds, the program is still relying on one effective mode of action.
The number of products, active ingredients or groups on the label does not determine the diversity of the program. What matters is how many different modes of action are effective against the problem weeds. Check the active ingredients and herbicide groups on the label and confirm which ones control your problem weeds.
Rotation helps, but herbicide layering goes further
Herbicide rotation helps, but weed populations may still face only one effective herbicide group in a given season. Weeds that survive herbicide applications can then reproduce and become a larger part of the resistant population.
Layering goes further by using multiple effective modes of action at different times within the same season, including post-harvest, fall soil active, pre-seed and in-crop. When done correctly, it offers more complete control, meaning fewer survivors and less seed returned to the seedbank. Weeds that do escape or germinate after one pass can then be targeted in the next application with another effective mode of action. The key is to create multiple opportunities to control target weeds throughout the season.
The next step is to figure out how you can do that in your field.
What herbicide layering looks like in practice
To build a layered program, you need to think about the plan for the entire season long before you spray or seed.
Depending on the crop and target weeds, you may have opportunities to control weeds in the fall post-harvest, with a fall or spring soil-active application and at pre-seed or in-crop timing. A layered program uses different effective modes of action at more than one of these timings to manage the same weed populations throughout the season.
That does not mean every field needs an application at all four timings. Scout throughout the season to see what worked, identify where another layer may be needed and note what should be adjusted in future applications or seasons.
Fall soil-active applications, for example, can bring multiple benefits to a herbicide layering strategy. Not only can they use active ingredients or modes of action not used for in-crop herbicide applications, but they can also offer flexibility in the spring through early-season residual weed control. This means weeds that germinate later will generally be smaller and more susceptible to herbicides at pre-seed or in-crop timings.
“It really helps each subsequent application shine that much more when you can keep those populations down,” says Gullen.
Layering herbicides to manage kochia
Gullen has seen this approach work in fields where one application or active ingredient was previously being asked to manage heavy kochia populations. After reviewing the existing program, they identified where other effective modes of action could be added through different application timings, including a fall residual, a pre-seed burndown and a post-harvest application. Each added layer reduced the kochia population for the next application rather than leaving one pass to carry the entire program.
“With weeds like kochia, adding fall timing can make a big difference,” says Gullen. “Kochia populations can adapt very fast, and they’re quite competitive, so you can’t get full control in one year. You need to think a few seasons ahead when building a herbicide layering plan.”
Find the missing layer in your program
When building a herbicide layering program, a good place to start is identifying the problem weeds and reviewing the herbicide groups and application timings used in your fields over the past several seasons. Consider which modes of action have been relied on, where another active ingredient could strengthen control and where a different effective mode of action could further diversify the program.
“You get four times a year to tackle weeds—post-harvest, fall or spring soil residual, pre-seed burndown and in-crop,” says Gullen. “Look at what you can do to maximize each of those timings to tackle your specific problem.”
Not every field needs all four. Preserving today’s weed control options means identifying where another effective layer could strengthen control, reduce reliance on any one mode of action and prevent surviving weeds from returning seed.
Explore which soil-active herbicides could add another layer of control to your program: What soil residual fits your needs? | Nufarm Canada
