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Spraying a mix of Roundup and another product on soy fields in Wisconsin.

Spraying a mix of Roundup and another product on soy fields in Wisconsin.

Photographer: Jesse Chehak for Bloomberg Businessweek

Does the World’s Top Weed Killer Cause Cancer? Trump’s EPA Will Decide

Roundup has revolutionized farming. Now, human health and Bayer’s $66 billion deal for Monsanto depend on an honest appraisal of its safety.

Every year, farmers spray, on average, almost a pound of the herbicide glyphosate on every acre of cropland in the U.S., and nearly half a pound on every acre of cropland worldwide. Glyphosate is the active ingredient in Roundup, a huge source of income for its manufacturer, Monsanto Co., and the foundation for its epochal foray into genetically modified organisms. If you know nothing else about GMOs and Monsanto, know this: The St. Louis-based company reengineered the DNA of corn, soybeans, and other crops for the primary purpose of making them resistant to Roundup.

Farmers spray the chemical on crops grown from Monsanto’s Roundup Ready seeds. The weeds die, harvests expand, and expensive, laborious tillage is no longer necessary. Large-scale agriculture is built on this model, and not only in the U.S., which is why Bayer AG, the German drug and chemical company, agreed in September to buy Monsanto for $66 billion, pending regulatory approvals. Other than government antitrust objections, about the only thing that could mess up the purchase would be for the U.S. Environmental Protection Agency to reverse its position on the active ingredient of Roundup, glyphosate.