Many corn farmers go back to using chemicals as Mother Nature outwits genetically modified seeds23/05/2013 15:08
Insecticide sales are surging after years of decline, as American farmers plant more corn and a genetic modification designed to protect the crop from pests has started to lose its effectiveness.
The sales are a boon for big pesticide makers, such as American Vanguard Corp. and Syngenta AG. But it has sparked fresh concerns among environmental groups and some scientists that one of the most widely touted benefits of genetically modified crops—that they reduce the need for chemical pest control—is unraveling. At the same time, the resurgence of insecticides could expose both farmers and beneficial insects to potential harm.
Until recently, corn farmers in the U.S. had largely abandoned soil insecticides, thanks mostly to a widely adopted genetic trait developed by Monsanto Co. that causes corn seeds to generate their own pest-killing toxins, but which the Environmental Protection Agency says doesn't hurt humans.
The modified seeds, first introduced in 2003, proved to be largely effective against the corn rootworm, a voracious bug that is the main scourge of the nation's largest crop. Today, according to the U.S. Department of Agriculture, two-thirds of all corn grown in the U.S. includes a rootworm-targeting gene known as Bt.
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.