Just a few years ago word broke that corn rootworms were breaking through GMO-resistance in a few fields in Iowa and Minnesota. The fields had one thing in common- most, at least at first, had been in continuous corn for several years, and the same rootworm trait had been used year after year.
Last year word of an outbreak in a county in central to east-central Illinois captured the headlines. So far no corn rootworm resistance has been documented in Indiana. The only trait that has not controlled corn rootworm effectively in these other areas of the Corn Belt is Monsanto's cry3Bb1 trait.
Steve Gauck, an agronomist for Beck's Hybrids, based in southeast Indiana, says the goal is to keep Indiana free of corn rootworm resistance issues. He offers several steps that should help prevent corn rootworm resistance from showing up here.
"The first step is to rotate crops," he says. "There is an advantage to a corn and soybean rotation.
"Second, you need to control volunteer corn in soybeans, especially if it was GMO corn with the rootworm trait. The volunteer corn may have some level of the protein, but not enough to kill off larvae. Some might survive."
Third, consider selecting hybrids that stack rootworm events in the hybrid. In other words, there is more than one mode of action to kill rootworms. When there is more than one mode of action it is more difficult for rootworms to develop resistance. You can also select hybrids that have rootworm traits pyramided on top of each other, he says. This means there are at least three traits in the hybrid that can control corn rootworm larvae.
Finally, it's important to practice refuge requirements. While there is no documentation many believe that many farmers were lax on this requirement when they were supposed to leave strips of non-GMO corn for refuge.
The new hybrids are typically refuge-in-a-bag, either at 90-10 or 95-5%. Hybrids with three rootworm traits will definitely be 95-5, meaning 95% of the seed is GMO and only 5% is a non-GMO hybrid susceptible to the rootworm.