Some cornfields in Iowa are now silking. And even though the state's farmers had a longer planting period than usual this year because of the wet spring, most cornfields will be well into the reproductive stages shortly. Tristan Mueller, program manager for the Iowa Soybean Association's On-Farm Network, says now's the time to be watching your fields for adult corn rootworm beetles.
"Beginning with your continuous cornfields, scout now to make counts of the adult beetles, to get an idea of the population of beetles present in your fields this summer," Mueller advises. "You need to scout and get an estimate of the beetle population even if you planted a corn hybrid that has Bt resistance to corn rootworm.
"Last year, we documented high levels of root damage and silk feeding in several corn-on-corn fields planted with hybrids that had Bt rootworm traits," says Mueller. He says root damage may be high, even in Bt RW corn hybrids, if egg-laying was heavy in that field the previous year. Taking beetle counts now will tell you whether silk clipping could be heavy enough to reduce yields.
Stalk lodging was caused by corn rootworm damage in this 2012 cornfield that was planted to a Bt RW corn hybrid.
Over the next week or so, Iowa State University crop scouts will be checking fields where ISA On-Farm Network corn rootworm replicated strip trials are located, so it's important for participating farmers to get their applied data submitted for these fields.
Possible rootworm resistance to Bt traits in corn hybrids is raising questions from farmers
Mueller says there have been several questions from farmers about rootworm resistance to Bt traits expressed in corn hybrids. The corn hybrids have the traits that are supposed to limit rootworm damage, but some farmers are seeing root damage in these fields. "If you planted a Bt RW corn hybrid, counting beetles now and monitoring for root damage later will tell you whether there's a possibility that the corn rootworm population in your field is resistant to the trait," Mueller says.