Mercedes Diaz tramps into a muddy soybean field and runs her brightly manicured fingers through the limbs of dozens of knee-high plants. As she checks the stems, pods and leaves, she rattles off a list of possible maladies under her breath: pod borers, frogeye leaf spot, white mold. Diaz spots a tangle of mottled leaves and shouts, “SDS!”—signaling sudden death syndrome. She plucks one of the leaves and hands it to me. I turn the crinkly, palm-sized leaf over in my hand. Irregular holes riddle its surface, along with ugly brown spots tinged in yellow—the effects of a toxin produced by the SDS fungus that courses through the plant, robbing it of its pods and chewing up the leaves from the inside out. SDS is one of the top crop killers in the U.S. According to the United Soybean Board, it cost farmers more than 60 million bushels in lost yields in 2014. And yet Diaz could not be happier to see it in her field.