While lots of labels tout their lack of genetically modified ingredients, if California's Prop. 37 succeeds, foods containing GMOs would have to be labeled. Paul Sakuma/AP hide caption

itoggle caption Paul Sakuma/AP

Central Illinois corn and soybean farmer Gary Niemeyer readies his genetically modified seed corn for spring planting at his farm near Auburn, Ill. Seth Perlman/AP hide caption

itoggle caption Seth Perlman/AP

Italian farmer Giorgio Fidenato picks up what's left of his genetically altered corn after anti-GMO activists trampled it, back in 2010. Paolo Giovannini/AP hide caption

itoggle caption Paolo Giovannini/AP