Authority herbicides are now registered for conventional and Roundup Ready soybeans, giving Manitoba farmers the option for residual weed control and another tool to delay the onset of glyphosate-tolerant weeds, including kochia.
Authority (sulfentrazone) can be tank mixed with glyphosate and applied pre-plant surface or pre-emergent surface to control kochia, lamb’s quarters, red root pigweed and wild buckwheat.
Authority Charge (cafentrazone and sulfentrazone) should be tank mixed with glyphosate and applied pre-plant surface.
Both products were already registered for use in chickpea, field pea, flax and sunflower.
“This is a timely registration for soybean growers in the Prairies with the identification of glyphosate-resistant kochia in the Red River Valley region of Manitoba and other soybean-growing areas,” Nasir Shaikh, Manitoba Agriculture, Food and Rural Development’s (MAFRD) weed specialist, said in a news release issued by FMC Canada.
“Authority is a strong kochia product so growers can use it to help prevent kochia from spreading.”
Using Authority can reduce the number of glyphosate applications in a single season, which can delay the development of glyphosate-resistant weeds.
Authority controls a number of small-seeded, broadleaf “flushing” weeds that germinate in the top inch of soil, Brad Ewankiw, a Winnipeg-based FMC Canada account manager, said in an interview May 22.
“What we want is for growers to spray the product on the surface of the soil and not incorporate it because we don’t want to dilute it to more than within that inch,” he said. “It has to be in a soil solution for those emerging weed seeds to take it up in their roots. The small-seeded weeds need a rainfall to get germinated, we need a rainfall to be activated — those things happen at the same time. The product is taken up by weeds as they are germinating and are controlled before they emerge.”
Tank mixing with glyphosate controls many of the weeds already emerged at the time of application.
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For years, weed scientists have urged farmers to rotate herbicides to delay the development of herbicide-tolerant weeds, but most agree applying a tank mix with different modes of action is even better.
Glyphosate-tolerant weeds are expanding in the United States.
“We’re confident the use of products like Authority in Roundup Ready soybeans, and other modes of action in other Roundup Ready crops, can really help to delay the onset of those resistant weeds coming into Canada,” Ewankiw said. “Let’s be proactive and not reactive. I think if you asked any grower in the U.S. if they could go back and be proactive they would because it is causing a lot of problems for them now.”
Using Authority will provide six to eight weeks of weed control, depending on the species, which could mean one or two fewer passes with glyphosate, he added.
“Those are huge cost and time savings for growers who are already struggling to get everything done,” Ewankiw said.
Authority costs $13 to $19 an acre, depending on the rate, which is affected by the soil type, pH and weed spectrum.
“If we can skip an in-crop application of glyphosate you’re almost even on the cost side,” he said. “And the benefits of utilizing a new mode of action and the yield benefits of keeping the crop clean early… are going to turn this into a much better economic situation than breaking even.”