Although the use of corn hybrids with Bt traits and seed treatment insecticides have improved the control of early-season corn pests, controlling pests once corn has reached knee high to harvest still requires scouting and managing outbreaks to preserve yield.

University and company researchers in the western Corn Belt remind producers and retailers to remain watchful for various pests in case they reach economic thresholds for treatment.

Pests To Watch This Summer
Jeff Whitworth, Extension entomologist at Kansas State University, warns growers to watch for southwestern corn borer.

"Southwestern corn borer has become more of a problem in the southwest quadrant of Kansas and has moved up into the north-central part of the state in the past four to five years," he said.

He also included fall armyworm (which has been an occasional pest in Kansas), armyworms, corn leaf aphids and grasshoppers to the list of pests that could be problematic mid to late season. He mentioned that western bean cutworm has been a problem in the western side of Kansas. WBC can affect the corn during tasseling.

Jon Tollefson, entomologist, Iowa State University, agreed that WBC could be a problem in Iowa as well. He reminds growers that WBC isn't controlled by every Bt on the market. "Western bean cutworms need to be watched at silking because if they get down into the whorl they become very difficult to reach with insecticides," Tollefon said.

One distinction Tollefon pointed out is that corn earworms are cannibalistic whereas WBC is not. "This means that corn earworms will fight to be the one earworm on the ear and eat its competitor, but WBC are not cannibalistic. Therefore their chances of survival are greater because they aren't controlling themselves."

Tollefson also added that corn ear worms and spider mites could also be pests to watch mid to late season.

Extension entomologists in high corn rootworm areas also suggest adult corn rootworms can do extensive damage.

Only the larvae are controlled by Bt corn. There will be survivors. Some of them will come from the same field and others will be flying beetles from other fields. However, the presence of corn rootworm adults does not mean the Bt seed didn't work, both seed company and Extension entomologists explain. Some farmers' perception has been that using the Bt trait would control all corn rootworm through adults. But that's not so."

Aphids are sometimes mentioned as corn problems too-corn leaf aphids, English grain aphids and bird cherry-oat aphids. All three of these species have been showing up more in the late season, according to scouting reports from the past couple of years.

Too Much Reliance on Bts?
One thing researchers agree on is that farmers have become very reliant upon the Bt technology and seed treatments to control early-season pests in corn.

Some entomologists are concerned that over-reliance on one technology will create resistance even to Bt. These entomologists have expressed it's not a matter of if but when.

FMC is a company that has specialized in insect control through insecticides. It's technical service specialists have seen major shifts in insects and control methods during the past 30 plus years.

"It is human nature for producers to want to simplify the way they produce a crop," said Bob Hooten, Midwest technical support manager, FMC Corporation. "However, easy doesn't always mean it's best. As everyone adopts a technology, it becomes worse for shortening the life of the tool. Look at Roundup. The same thing is happening with Bt. Everyone is adopting it.

"As growers utilize new technology, whether it is a chemical pesticide, genetic trait or seed treatment, Mother Nature adjusts by shifting the pest spectrum, establishing resistance or opening a niche to a totally new pest. Examples of this are abundant," Hooten said.

Hooten used soybeans as an example of expanding insect concerns. Soybeans are becoming a major crop for insecticide use as populations rise for soybean aphids, bean leaf beetles (which spread bean pod mottle virus), stink bugs, soybean stem borer, Japanese beetles and others.

Hooten explained that in the past, as some companies were changing their strategic offerings to include more insect control through genetics as opposed to insecticides, the Environmental Protection Agency was putting pressure on other companies with insecticides to go to enclosed application boxes, remove registration tolerances or shift to all liquid with no granular formulations available.

The EPA has shifted toward putting insecticide control more in the hands of genetics. Hooten is concerned that there will not be enough insecticides registered and marketed to be effective rescue treatments when genetics begin to fail.

Protecting the Technology
A way to help prolong the use of the genetic technology is to not use it if it's not needed. Both Hooten and Whitworth agree that it may be more economical for some growers to consider using non-Bts in some cases and rely on mid-season insecticides.

"Most of the insecticides used to control your mid- to late-season pests will also work on the early season pests," Whitworth said. "So, it might be better to wait and spray later because you'll be saving the money that would have been spent on the seed trait."

Hooten pointed to the example of the rise over the past couple of years in non-GMO soybeans. As glyphosate-resistant weeds have made farming soybeans more difficult, having the option to use other herbicides has begun to be accepted by a portion of the soybean growers.

Ten years ago, some researchers suggested growers didn't need anything but Roundup, which simplified the production process. The challenge today with Bts is that no one has been able to really test if resistance is building up within this technology, Hooten said. "The insect spectrums are shifting. We're seeing more rootworm adults surviving.

So, something is happening. Is it resistance or adaptation? We don't know."

Another pest that's becoming more of a problem as farmers switch to genetics instead of fumigants or insecticides is nematodes.

"None of the genetics in seed control nematodes," Hooten said. "What's going to happen in corn and soybeans in a few years when there's nothing to control nematodes?" he asked. "Farmers' options are becoming more limited.

However, we believe that there will always be new markets for companies that stay ahead and plan ahead," he said.