Contributed by Chandra Montgomery & Albert Adjesiwor, University of Idaho
There’s no doubt that growers rely heavily on glyphosate for weed control. For no-till dryland small grain growers, glyphosate is an important herbicide for pre-plant and post-harvest weed control. However, the repeated use of glyphosate as the main weed management tool is resulting in widespread glyphosate-resistant weed populations. To protect the value of glyphosate in small grain production systems, it is important to identify effective alternative herbicides and mixtures for weed control.
The value of glyphosate to growers practicing minimum or no-till has been primarily a function of three factors: improved weed control (especially grassy weeds) with glyphosate compared to other herbicides; lack of residual effect or injury from glyphosate; and relatively cheap cost of glyphosate (or maybe not anymore). Thus, any possible alternatives to glyphosate must satisfy at least some of these conditions if they were to be adopted by growers.
Over the past three years, we have been evaluating several herbicides and herbicide combinations to find herbicides that satisfy the criteria for the “ideal” pre-plant burndown herbicide. By “ideal” we mean it must be: effective and provide broad-spectrum weed control, leave little to no residue in the soil or not cause injury to wheat/barley, and be economical (relative to glyphosate). Specifically, we wanted to answer three questions:
- Are there effective alternatives to glyphosate for pre-plant weed control?
- Are there safe alternatives to glyphosate for pre-plant weed control?
- Are there economical alternatives to glyphosate for pre-plant weed control?
With that in mind, we chose herbicides that we think may satisfy these conditions (See table below). We also considered the cost of these herbicide programs. Please note that prices are rapidly changing so these are just approximate costs for comparison purposes.
Herbicide rates and approximate cost of herbicide programs
Weed control efficacy and crop safety
What we have found so far is promising. We found several herbicides or herbicide combinations that provided good kochia and green foxtail control (Figures 1 & 2). No crop injury was observed after crop emergence, and we did not see any crop yield reduction from the herbicide treatments.
Figure 1. The efficacy of herbicide programs on kochia. The vertical dashed red line corresponds to 90% control.
Figure 2. The efficacy of herbicide programs on green foxtail. The vertical dashed red line corresponds to 90% control.
Circling back to our research questions;
- Are there effective alternatives to glyphosate for pre-plant weed control?
The answer is YES, there are effective alternatives that provided 90% or more control of broadleaf and grassy weeds.
- Are there safe alternatives to glyphosate for pre-plant weed control?
The answer is YES, no significant injury was observed, and barley and wheat yield were not affected by herbicide treatments.
- Are there economical alternatives to glyphosate for pre-plant weed control?
YES, there were herbicide treatments that provided effective weed control and were as economical as glyphosate.