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Non-Bt cornfields hit hard by corn borers

In late June, some non-Bt cornfields in Arkansas were hosting massive, first generation corn borer populations. “Some fields are seeing severe infestations,” said Jason Kelley, Arkansas Extension corn specialist. “That’s particularly true in scattered northeast Arkansas fields. Growers there are worried about lodging.”

But the problem isn’t uniform. “In some non-Bt fields you have to hunt to find a borer. Like most insects, it’s variable in regions. But, where the borers are heavy, they’re extremely heavy.

“In fact, the first generation numbers being seen in some fields are higher than what we’d expect to see in a bad second generation problem.”

Roger Gipson, Pioneer agronomist, said he’s “never seen anything like what’s happening in some of the cornfields. I’ve been in non-Bt fields that are absolutely overrun. Growers who planted non-Bt corn need to be alerted to this.”

Glenn Studebaker, Arkansas Extension entomologist, agreed. “The worst problem fields I’ve seen have been on the west side of Crowley’s Ridge.

“I was in a field in Randolph County that was absolutely eaten up with them. It’s strange where they hit, though, because a half-mile down the road a non-Bt field planted the same day only had a few.”

Fields around Des Arc in Prairie County have also been hard hit.

The most severely affected fields have both stalk tunneling and whorl feeding on the same plants.

“In the bad cases, I bet 90-plus percent of the plants are infested with the first generation,” said Gipson. “One field I checked was so bad the pest had actually stunted the plants.”

What about treatment options? “At this stage of the game with first generation corn borers, there’s little that can be done,” said Kelley. “Once they’re in the stalk, they’re safe.

“I suspect in the next couple of weeks that second generation will hatch in the northeast and an insecticide can go out to try and keep the problem from getting worse.”

Studebaker said the second generation is already beginning to emerge in the south and central parts of Arkansas. “We’ve got pheromone traps all along the Delta. The timing of the insecticide application is very important. They’ll hatch and may feed for a few days on the leaves and they’re still vulnerable to an insecticide. Once they bore into the stem, though, there’s nothing we can do. It is imperative an insecticide is put out in time.”

Growers and consultants in central and southern Arkansas “are being advised to scout their non-Bt fields and look for eggs and small worms.”

The problem is the treatment timing isn’t an exact thing. The second generation won’t emerge all at once, “so you need to time it to catch the bulk of the population,” said Kelley.

Pyrethroids typically provide three or four days residual control, at most. “If it’s put out too early, it’ll be gone before the eggs are laid and hatched,” said Studebaker. “Many growers are leaning towards Intrepid. It has a bit different chemistry and a residual of two or three weeks. There’s a little more wiggle room with that product.”

Meanwhile, the corn crop is largely disease-free and doing well. “Overall, the irrigated corn looks good,” said Gipson. “I’ve done a few yield estimates and looked at ear sizes and the crop looks promising.

“We do have to watch out for the non-Bt hybrids, though. I don’t want to paint a picture that corn borers are eating through every non-Bt field. But there’s enough of them in enough fields that it wouldn’t be right to say there aren’t serious concerns.”


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