Monsanto and the University of Missouri are in the process of investigating a potential case of glyphosate-resistant common ragweed on a single field in central Missouri. Preliminary findings of field and greenhouse trials indicate lack of control; however, additional factors such as hereditability, insect interactions, and the unique morphology of this population all raise additional questions that merit further research.

“At this point, we are seeing a difference in control of common ragweed in one isolated field, though there have been no other complaints locally and excellent control in other parts of the state” said Dr. Reid Smeda, University of Missouri weed scientist. “We are researching factors that may be playing a role in this specific situation.”

It’s critical that growers use the right rate of glyphosate for the right size weed at the right time, as well as additional weed control tools that may be necessary for the weed spectrum on their farm. The vast majority of weed performance inquiries are due to improper application or environmental conditions.

“Monsanto takes product stewardship and customer service very seriously,” said Kerry Preete, Vice President of U.S. Crop Production for Monsanto. “We are working with academic experts to investigate this situation very thoroughly and provide practical recommendations for growers.”

The development of resistance to glyphosate is less likely compared to other herbicides. Only two weeds have been confirmed resistant in the US, one of which is in a non-Roundup Ready crop system, after nearly thirty years of commercial use. These cases have been effectively managed with tank mixes. Similar measures, such as Roundup tank mixed with FlexStar or Phoenix, will be put in place should this common ragweed biotype prove to be resistant. As part of its ongoing stewardship program, Monsanto recommends that growers follow sound agronomic principles and report instances of unsatisfactory weed control to their sales representative for follow up.

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