This summer, a severe drought and genetically modified crops are delivering a one-two punch to US crops.

Across the farm country, years of reliance on Monsanto's Roundup Ready corn and soy seeds—engineered for resistance to Monsanto's Roundup herbicide—have given rise to a veritable plague of Roundup-resistant weeds. Meanwhile, Monsanto's other blockbuster genetically modified trait—the toxic gene of the pesticidal bacteria Bt—is also beginning to lose effectiveness, imperiling crops even as they're already bedeviled by drought. Last year, I reported on Bt-resistant western rootworms munching on Bt-engineered corn in isolated counties in Minnesota, Iowa, and Illinois.