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Following reports of high levels of corn damage in Iowa, lab studies this summer revealed resistance to Bt hybrids expressing the Cry3Bb1 toxin, found in Monsanto hybrids targeting rootworms.
Field locations where resistance was documented were characterized by high rootworm pressure, with a history of continuous Bt corn planting, says Iowa State University entomologist Aaron Gassman. While this wasn’t considered a widespread threat, Monsanto says it’s working with Gassman on how to handle the apparent resistance.
University of Illinois Extension entomologist Mike Gray also verified severe corn rootworm pruning on some Bt hybrids that express the Cry3Bb1 protein in northwestern Illinois.
The fields were in continuous corn production for many years and producers relied upon Bt hybrids that expressed Cry3Bb1 protein as their primary protection against western corn rootworm injury.
Gray urged no-tillers to be cautious in their choice of hybrids offering corn rootworm protection.
“Many producers have utilized a single-tactic approach for too many years,” he says, “and now unfortunate consequences are beginning to emerge.”