Most agree, though, that it will take more than simply adding new herbicide options to the weed-fighting arsenal. Some see a diverse mix of herbicides and frequent crop rotation as one answer.

But others say it’s more likely farmers will be forced to revisit some of the strategies retired in the 1990s. It could mean more hoeing of fields, more tillage, and planting of cover crops to keep fields blanketed and less hospitable to weeds.

“I don’t think we are going to find the solution to the resistance in the bottom of a jug,” said Kevin Bradley, an associate professor and weed expert at the University of Missouri-Columbia. “We have to go back to the way we used to think about weed control.”

It doesn’t help matters that there is a relatively new menace spreading north and threatening Midwestern fields.

Palmer amaranth is an aggressive, fast-breeding weed that can grow up to 10 feet high, with stalks thick enough to damage harvesting equipment. It’s a plant that’s been described as “waterhemp on steroids” or “a superweed before it became herbicide-resistant.”

And now that there are varieties of the plant with glyphosate resistance, academics such as Hager, from the U of I, are warning farmers to be vigilant. A single weed in a field is too many, they say.

“There is no acceptable level of Palmer infestation,” he said. “It is a species that has, quite literally, put farmers out of business.”

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