Overuse of this seductively simple approach to weed control is starting to backfire. Use of Roundup, or its generic equivalent, glyphosate, has skyrocketed to the point that weeds are rapidly becoming resistant to the chemical. That is rendering the technology less useful, requiring farmers to start using additional herbicides, some of them more toxic than glyphosate.

“Farmer practices may be reducing the utility of some G.E. traits as pest-management tools and increasing the likelihood of a return to more environmentally damaging practices,” the report concluded. It said the problem required national attention.

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