The black cutworm threat is receding in this part of the state, but the threat from corn rootworm is just now getting started.
Both pests love to munch on the roots of corn plants, and Purdue agricultural extension educators like Tipton County’s Jeff Wessell spend considerable time in fields, trying to get a grip on how prevalent the insect larvae are in a given year.
Farmers, armed with corn hybrids specifically resistant to cutworms, corn rootworms and corn borers, are usually up to the task of controlling the pests, but nature, Wessell notes, is a wily foe.
Many farmers will use corn infused with a genetic trait drawn from Bacillus thuringiensis, a bacterial strain which naturally produces a protein fatal to borers and rootworms.
The genetically modified corn has been around for more than a decade and has proven remarkably effective in curbing the European corn borer, a pest that used to devastate local crops.
Scientists isolated the Bt protein in the mid-1990s, and companies like Monsanto and Syngenta were soon making insecticides based around the protein. By the early 2000s, scientists had figured out how to graft the trait into seed corn, so the plant itself now produces the protein.
Those were massive advances against corn pests, Wessell said, but rootworms have proven resistant, moreso than borers.
Some farmers not only use transgenic Bt seed corn, but also use seed-applied insecticide, and then granular insecticide as well.
“That’s a lot of resources,” Wessell said. “When you target one pest, it disadvantages the farmer economically, and eventually, the pest will overcome all those tactics, and then it will be difficult to find a new way to control it.”
Corn rootworm managed to overcome crop rotation about a decade ago, Wessell noted. Farmers used to be able to control the pest by simply planting corn after soybeans, since the adult moths didn’t lay their eggs in soybean fields. But the resilient insects figured that one out.