Seiter, an entomology specialist with the University of Illinois, said the introduction of Bt hybrids around the year 2009 have lowered populations of corn rootworm in the Midwest, and particularly in Illinois. However, that doesn’t eliminate concern about what he called Illinois’ “most important insect pest” in corn.
“Of course, resistance development with that insect is a constant concern,” Seiter said. “We are starting to see more damage to some of these trait packages, especially in northwestern Illinois. We saw quite a bit of that last year in comparison to previous years.”
He said a gradual increase of corn rootworm resistance is to be expected, as with any weed or pest.
Helping combat those resistances, Bayer is preparing to introduce a new trait to the marketplace with SmartStax PRO technology. In 2022, the company is introducing the third generation of corn rootworm protection.
Jody Gardner, Bayer’s North American technology development manager for corn traits, said the technology uses RNAi to combat corn rootworm.
“This can target specific pests, such as corn rootworm,” Gardner said. “It’s based on bt proteins. They have proven to be very effective proteins over the years.”
Gardner said the technology will also protect against corn borers, fall armyworm, black cutworm and corn earworms.
Ahead of planting, Seiter said it’s difficult to take much action to combat corn rootworm. Much of the damage done by the pest won’t be seen until the summer, and eggs aren’t likely to hatch until late May or early June. Right now, farmers need to start developing a plan for what they will do if corn rootworm shows up in their fields.
“Know what hybrids you’re using and what soil insecticide you are using,” Seiter said. “Get that background information together to assess the situation. By mid- to late June, you can sample fields for the larvae.”
He said adults will typically emerge around the Fourth of July. He encouraged farmers to take that time to scout for corn rootworm, evaluating any damage done to the roots. From there, farmers can start to take action.
“If it gets bad enough, you’ll get lodging and have plants fall over,” Seiter said. “We want people to look at that in the middle of the summer, while the plants are still alive. By the time the plants have matured, it can be a little more difficult to decide if it’s corn rootworm or other factors that are causing plants to fall over.”
Gardner said there is no hard-and-fast threshold for determining how much pressure is needed before using treatment, but noted that many farmers who have dealt with the insect know it can be a significant drag on the crop. He suggested going to local resources, such as university extensions, to determine when the best time to spray would be.
For those making plans for the insect, Seiter said this is a problem that often stacks on itself. If corn rootworm left a lot of damage in the fields last year, one can expect more damage this year if left untreated.
“Beetle numbers last year are the No. 1 indication of how much egg lay could be going on in those fields,” he said. “If you had higher than expected damage in a package last year, there’s a pretty good chance you’ll see more of the same in the coming years.”
