Economics has been one reason farmers have chosen to plant corn on corn, year after year. While corn-on-corn cropping systems have been profitable, they do require extra rootworm management for long-term success.
Jim Stara of David City farms around 4,500 acres of row crops with his family. He takes a multifaceted approach to beating corn rootworm problems that arise in corn-on-corn situations.
Stara, who spoke to a group of producers and crop consultants as part of a farmer panel at a corn-on-corn clinic in Norfolk recently, said that hybrid selection for the right Bt corn seed is a key management decision that begins the year before. Then, Stara scouts fields regularly, and has treated for western corn rootworm beetles at silking time to prevent silk clipping. "If I see enough beetles later on, I will hit them again," he says.
Monitoring the field situation for corn rootworms is crucial to getting the treatment timing right, says University of Nebraska Extension entomologist, Bob Wright, who also spoke at the workshop. He says that crop rotation at least once every three or four years will reduce rootworm densities and make Bt corn and insecticides work better.
Selecting new pyramidal corn varieties that carry two Bt proteins to fight corn borer and two Bt proteins to fight corn rootworm will "make it harder to develop resistance," he says. "Rotate insecticides and different Bt proteins over time."
Wright says, "Resistance doesn't mean it is totally immune. It is just harder to kill." The longer a farm grows the same hybrid in the field, the more resistance that will develop by the rootworms.
"We've been talking about resistance for 10 years," Wright says. Corn rootworms have shown resistance to a variety of control methods since the 1950s, he says. A combination of Bt corn seed, planting time insecticides, summer time monitoring and treatment of adult beetles during the growing season will provide a strategy to keep densities low and damage minimal.
Recent hot weather has probably had an impact on the longevity of adults, Wright says. They have also most likely laid their eggs deeper in the soil than usual.
If you'd like more information, contact Wright at 402-472-2128 or email firstname.lastname@example.org.