Today, there are several management strategies that can help you tackle the most problematic weeds and delay the spread of herbicide resistance.

Among the most effective is herbicide layering — planning your applications so that multiple modes of action are used in sequence over the course of a growing season.

One way to do this is to replace or supplement a foliar application with a pre-emergent, soil-applied herbicide in the fall or early spring.

“The message that producers have been getting is to tank mix your in-crop herbicide. Herbicide layering takes it one step further by using a soil-applied herbicide in addition to a tank mix,” said Haley Stratichuk, AAg, a Co-op Grow Team agronomist in Saskatchewan’s black soil zone outside Yorkton, Sask.

“A lot of the pre-burn products that are on the market involve the same modes of action that are used in later in-crop applications. A soil-applied herbicide can help address that issue so you don’t have that overlap.”

Start with soil-applied

Several soil-applied herbicides are available today ahead of most crop types, including many older products, such as Avadex® (Group 8) and Edge™ (Group 3). Avadex provides control of wild oats, while Edge provides suppression of both wild oats and cleavers — weeds that are regularly resistant to more commonly used modes of action.

Among other products, Command® (Group 13) has become a popular choice for cleaver control in canola. Fierce®, registered for soybeans and spring cereals, is another interesting option, combining two modes of action — Groups 14 and 15 — for control of several problematic weeds.

These soil-applied products provide a residual effect over the first few weeks of the season and help to keep weed populations as low as possible, which sets you up for a more effective in-crop application.

“Weed resistance tends to show up in fields with higher weed populations, so it’s important to start clean and stay clean,” said Stratichuk.

“When you start clean, your yield benefit really increases, because you don’t have that weed pressure on your crop. As soon as you have weeds, even if you don’t think you have a lot of them, they’re still competing with your crop in some form.”

Mix it up

Following a soil-applied herbicide, your in-crop application should incorporate products with different modes of action from your first application. For example, when planting InVigor canola, you may consider a pre-seed application that includes glyphosate (Group 9) and Command and following up with an in-crop application of Liberty (Group 10) and clethodim (Group 1).

By using two to three different effective chemistries in this manner, you can see improved weed control, which will reduce the selection pressure that produces herbicide resistance.

“I think the main thing is to be aware that resistance is out there,” said Stratichuk.

“Even if a grower thinks he doesn’t have resistance, you kind of have to act like you do, just so you can protect yourself down the line and protect the future of those fields.”

Soil-applied herbicides are one way you can bring herbicide layering to your farm. To discuss all product options and strategies, speak with your Saskatoon Co-op Ag team member who can help you build a plan to address the unique challenges in each of your fields.