Tank-Mixing Herbicides May Not Be Enough to Avoid Herbicide Resistance
Several years ago, University of Illinois and USDA-ARS scientists turned weed control on its head, writes Lauren Quinn at University of Illinois, College of Agricultural, Consumer and Environmental Sciences (ACES). More and more herbicide resistant weeds were popping up, and the pest plants were getting harder to kill. It was clear farmers could no longer rely on the same chemicals year after year. Industry campaigns and herbicide applicators began touting the benefits of rotating herbicides annually to avoid developing resistance, and rotation quickly became common practice.
But in 2015, a team of weed scientists from U of I and USDA-ARS studied the effects of herbicide rotation and found the practice actually increased resistance to glyphosate in waterhemp, a common and destructive Corn Belt weed. What worked, instead, was mixing multiple herbicides in the same tank and spraying simultaneously. Their large experiment, including 105 grain fields across Illinois, showed tank-mixing was 83 times less likely to lead to glyphosate resistance.
The study had a powerful impact, with recommendations changing nearly overnight; tank-mixing herbicides is now de rigueur. But one of the study’s authors is now urging farmers and industry players to remember tank-mixing only delays the evolution of resistance.
“I worry this practice has become overused. It’s too simplistic to think all you need to solve the challenges of resistance is to go on using herbicides but in a slightly different way,” said Aaron Hager, weed scientist and faculty Extension specialist in the Department of Crop Sciences, part of the ACES at Illinois. Hager wrote about the topic in this farmdoc article.
He notes waterhemp is now resistant to herbicides from at least seven herbicide modes of action, despite the advantages of tank-mixtures. And some waterhemp populations are resistant to herbicides to which they have never been exposed. In other words, herbicide resistance is a complex and fast-moving target. And we’re not keeping up.
Continue reading at U of I ACES.
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