Managing Metabolic Resistance in Weeds
Dealing with herbicide-resistant weeds is nothing new for row-crop producers in MFA’s trade territory. Most of us in the farming community, writes Doug Spaunhorst, MFA Director of Agronomy, have faced these rebellious weeds one way or another for an entire career — or even a lifetime, if you were born after the mid-1980s. Waterhemp, for example, has shown evolving tolerance to many major herbicide sites of action that we use to manage weeds in row crops.
If this is a familiar issue, why write about it? Simply put, we’re seeing resistance become more complex, requiring us to take weed management up a notch. Many herbicides that were effective are now less or not effective at all when applied after waterhemp has emerged. In most reported cases, resistance is linked to a single, specific mutation at the target site in the plant’s DNA. As a result, herbicides such as Pursuit, atrazine, glyphosate and Flexstar are no longer as effective on waterhemp as they once were.
Farmers have been managing this resistance by returning to soil residual herbicides. Mixing multiple modes of action in the spray tank and overlapping those residuals have been excellent strategies. However, some waterhemp populations in the U.S. are breaking through certain residual herbicides with a different type of resistance — metabolic resistance.
Like human metabolism breaks down food, plant metabolism also processes substances, in this case, herbicides. In weeds that have developed metabolic resistance, the herbicide’s active ingredients are broken down into nontoxic byproducts that don’t kill the plant.
Metabolic resistance in weeds is not widespread, but the true extent is unclear. Researching herbicide resistance is a labor-intensive process that involves sampling and collecting seeds from suspected fields and evaluating them under greenhouse conditions. Regardless, producers and agronomic advisors need to be aware of metabolic resistance and what it could mean for their weed management program when they encounter it.
Read more at MFA.
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