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Is mixing herbicides in the sprayer enough to prevent resistance?
5/30/2023 9:56:41 AM

Is mixing herbicides in the sprayer enough to prevent resistance?

Eight years ago, when scientists at the University of Illinois and USDA-ARS made weed control a priority in the fight program, herbicide-resistant weeds were becoming more and more difficult to eradicate. It was clear that farmers could no longer rely on the same herbicides year after year. Therefore, they began to promote the use of herbicides on an annual basis to prevent resistance, and this method quickly became a common practice. But in 2015, a team of weed scientists at the USDA-ARS studied the effects of herbicide rotation and found that it actually increased resistance to glyphosate in bluehemp, a common weed that is destructive to corn. Their suggestion was to mix several herbicides in one tank and spray at the same time. Their large experiment, involving 105 grain fields across Illinois, showed that tank mixing resulted in up to 83 times less resistance to the herbicide glyphosate. This method of resistance control had a good effect and changed the previous recommendations overnight. The method of mixing herbicides in the sprayer tank is also popular now. But one advocate of the practice now urges farmers and industry activists to remember that tank-mixing herbicides only delays the evolution of resistance. For example, blue hemp weed is now resistant to at least seven mechanisms of herbicide action, despite the use of herbicide combinations. Some waterhemp populations have also become resistant to herbicides to which they have never been exposed. There are currently no data to test the hypothesis that herbicide mixtures are the most effective way to prevent the evolution of resistance mechanisms based on off-target sites. Without that data, how can we know which herbicides or combinations will remain effective against each bluehemp population? There is no easy way to answer this question. The problem of herbicide resistance is a direct result of over-reliance on a simple solution: chemical weed control. The problem will not be solved only by using the same tools, but in different ways. Instead, farmers should diversify tactics and focus on preventing or eliminating weed seed production. Although herbicides will continue to be a valuable tool to help prevent crop yield loss, we must also consider additional tactics to ensure that no weeds are allowed to set seed during the growing season. The only thing we know for sure is that if plants cannot produce seeds, no resistance mechanism will develop.

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