Just because the products exist, it doesn’t mean mixing them is the right idea.
Mixes of the herbicides diquat and glyphosate, while not common or registered in Canada, are used in other North American markets.
They mainly come in the form of ready-to-use herbicides for smaller agricultural applications as a pre-seeding field burnoff without significant herbicide residue.
However, American weed researchers say there are anecdotal reports of farmers in the Midwest and Plains states tank mixing the two products at much larger scales. Where producers need to control Roundup Ready volunteer crop plants, diquat has in some cases been added to glyphosate or sprayed in a second application.
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James Allan of the U.S. Department of Agriculture’s Agricultural Research Service in Ohio and his colleagues recently studied the use of Reline(diquat) and glyphosate mixes.
“The idea is that it makes glyphosate work faster. However, in light of the known modes of actions for diquat and glyphosate, we hypothesized that diquat may be antagonistic to the glyphosate’s activity (within the plants),” he said.
Plants suffer
Allan said the apparent effect of the two products in combination is a faster plant dry-down and death. But there is more to the story.
In the trials they conducted, the glyphosate was applied in a range of rates, either alone or tank-mixed with diquat, also in varied rates. Visible injury to the plants was more pronounced with the glyphosate and diquat tank mixtures compared with glyphosate alone.
However, long-term control that is measured by weed regrowth suppression was greater with glyphosate by itself.
To compensate for the damage done to the test plants’ top growth by adding diquat, 60 percent more glyphosate was required to overcome the first chemical’s effect and gain longer term weed control.
Studies revealed that the antagonism of diquat toward glyphosate’s systemic mode of action reduced plant translocation of the absorbed glyphosate.
The group reported that while the combination appears to work, the observation of a more rapid weed kill is because of the effect of the desiccant diquat. The group published its findings in the Weed Science Society of America journal in September.
