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.

This summer, resistant rootworms are back like the next installment of a superhero blockbuster movie franchise. In a July 30 post, University of Minnesota extension agents Ken Ostlie and Bruce Potter report they’ve seen a “major [geographical] expansion” of rootworm damage throughout southern Minnesota, where Monsanto’s corn is common. The severe drought, they add, has “masked” the problem, because rainstorms typically make rootworm-damaged corn plants fall over, and rainstorms haven’t come this year.

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Drought plus a plague of rootworms presents a compounded problem to farmers: The bugs tend to thrive under dry conditions, and the damage their incessant root munching does to plants above ground, like stunting their growth, is “magnified” by lack of water and heat stress, Ostlie and Potter add.