Soybeans are sprayed in Iowa in 2013. Enlist Duo is a mixture of two chemicals that farmers have used separately for many years: glyphosate (also known as Roundup) and 2,4-D. The new formulation is intended to work hand-in-hand with a new generation of corn and soybean seeds that are genetically engineered to tolerate sprays of both herbicides. Charlie Neibergall/AP hide caption

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Sunlight streams into a corn storage building at a Michlig Grain storage facility in Sheffield, Illinois, U.S., on Oct. 31, 2014. The price of corn has been falling for months. Daniel Acker/Bloomberg via Getty Images hide caption

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Empty shelves where eggs should be at a Whole Foods Market in Washington, D.C. The store blames increased demand for organic eggs. Dan Charles/NPR hide caption

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A corn field is shrouded in mist at sunrise in rural Springfield, Neb. Nati Harnik/AP hide caption

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President Obama and Agriculture Secretary Tom Vilsack (second from right) inspect drought-damaged corn on the McIntosh farm in Missouri Valley, Iowa. Carolyn Kaster/AP hide caption

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