Many corn farmers go back to using chemicals as Mother Nature outwits genetically modified seeds.
As more farmers switched to the modified seed, the share of corn acreage treated with insecticide fell to 9% in 2010, the most recent year for which data are available, from 25% in 2005, according to USDA data. Those farmers who continued to use insecticide applied less in 2010, the data showed.
In 2011, however, entomologists at Iowa State University and the University of Illinois started to document rootworms that were immune to the Monsanto gene, and have found these resistant pests scattered across the Midwest. Now, many farmers have decided they need to spray their soil to kill any rootworms that have developed Bt resistance, as well as growing populations of other pests.
Scott Greenlee, who farms 1,700 acres in Sac City, Iowa, said he planned to start using a soil insecticide this year after part of his crop succumbed to rootworms in 2012. The 53-year-old Mr. Greenlee, who had planted Monsanto’s Bt corn, said the affected fields produced just 50 or 60 bushels per acre, about a third of his normal yield. “It was a train wreck,” he added.