Farmers who plant Bt corn tend to get tunnel vision because of tunnels they don't see.

With the Bt gene warding off European corn borers, growers simply can't find the tell-tale tunnels of insect damage in their crop. It makes them take a narrow view of hybrids that end up on the ground by harvest.

Not only does the Bt technology work, it pays, according to growers who've tried Bt hybrids.

"In today's economy, you don't put it out there unless you know it will pay. You have to farm for net income," says Tom Mercer, Gibbon, NE. "I don't like paying an extra $25/bag. But, if that $25 returns $100, I'm going to put it out there.

"It all boils down to economics," says Mercer. "Bt corn is going to net $10 to $20/acre. Some years it will net $30/acre."

Three years of Bt corn have convinced Mercer that yield isn't a problem. His NC+ (5588) and Pioneer (35N05, 34R06 and 33A14) hybrids ranged from 197 to 213 bu/acre this fall on irrigated land. In a year of light corn borer pressure, his non-Bt hybrids did as well,averaging just over 200 bu.

"It was the one year in 15 that corn borer wasn't a real problem," Mercer says.

That won't keep him from planting at least 80% of his corn to Bt hybrids in 1999.

John Ward, Sycamore, IL, planted his first Bt corn in 1997. This grower liked the results so much he bought his '98 seed before Thanksgiving.

"Bt seed was in real short supply in our area in 1997," Ward reports. "We got enough to run test plots and plant one 112-acre field. We had high pressure last year. On a scale of one to 10, we were at seven to eight for borer pressure.

"Bt was unbelievable. We had varieties from Dekalb (580Bt) and Pioneer (35N05) in our test plots and one field. And even though the borer pressure was light, they ran 8-23 bu better than any other variety, regardless of maturity.

"In our 112-acre field, the Bt corn yielded 14 bu better than corn in a test strip," he continues. "You could see the difference as soon as you pulled into the field. We're used to getting 165- to 175-bu corn in that field. Last year we harvested 185 bu. We were impressed."

So impressed that Ward and his farming partner, son Stephen, "begged and pleaded with seed salesmen, wrote big orders and prepaid" to get enough Bt seed for 550 acres in 1998. He planted Dekalb 595Bt, 580Bt, 493Bt and 566Bt. He also planted Pioneer 33V08, 34R06, 35N05.

At press time Ward didn't have any yield data for this year's crop. Like Mercer, however, he expects non-Bt hybrids to fare as well as their Bt counterparts.

"I'd rate our corn borer pressure at two on a 10-point scale," Ward says.

"We had a great growing season and the insect pressure was very, very low. Normally we'd expect three out of five years to be bad for borers. We put the pencil to it last year, and we know it pays. You just have to accept the fact that, every few years, borer pressure will be light and you may not get as much return for the technology as you do other years."

Central Iowa farmers were reminded this year that you can't select for the Bt gene alone, even when yields match those of non-Bt hybrids.

High winds just ahead of tasseling caused heavy green snap losses this summer. Then pythium and anthracnose left many cornfields in September looking like it was October or November. The combination knocked at least 40 bu/acre out of some of those fields.

European corn borers or their damage, on the other hand, were difficult to find.

"Farmers in this area aren't convinced that the Bt hybrids are the best hybrids out there," says Ted Griffeon, Altoona, IA.

"The guys who spent the dollars for Bt this year didn't get much for it. People shake their heads when they have to pay the technology fee. With a light corn borer population this year, guys in this area are guessing that there won't be many overwintering and the population could be light again next year. They aren't convinced they'll make their money back."

Griffeon intends to continue to expand his Bt acres in 1999.

"We experimented with Bt in test plots in 1996. When we harvested the plots, the Bt corn was all standing while the plots around it were broken down. We knew we ought to take a look at more Bt hybrids."

This year Griffeon planted 80 acres of Mycogen 2787 Bt corn.

"It's real good corn. It even did reasonably well through green snap and high winds.

"We also planted Mycogen 7250, which has native resistance against borers. It stands well and really hangs onto ears. Next year it will be available with the Bt gene also. The combination should provide a double-whammy against borers."

Griffeon plans to expand his Bt acres in 1999 to roughly a fourth of his total production.

"I think we'll see some new hybrids that are high-yielding and better-standing," he says. "In heavy corn borer years, I think the Bt hybrids will yield 10-15 bu better than non-Bt hybrids. As better hybrids become available, I look to plant 80% Bt corn and use native-resistance hybrids for refuge."

South-central and western Minnesota growers are finding this fall that corn borer damage is worse than expected.

"Most growers thought it was a light year for borers, but we're finding up to 60% damage in some plots," says Pioneer agronomist Jim Boersma. "Bt hybrids are showing a yield advantage of 5-20 bu/acre. You can't predict infestations. It's why we recommend at least 50% Bt corn as an insurance policy."

The benefits of Bt go beyond yield protection, believes Nebraska's Mercer.

"When you spray for corn borers, you take out beneficial insects, too," he says. "I don't like to take out the lady beetles. They work on spider mites and will also eat corn borer eggs and small borers. There's also a hemp dogbane beetle that controls that weed."

Mercer and Ward like the protection that Bt provides.

"I've got enough livestock and crop acres to keep me busy," says Ward. I don't want to be in the fields scouting for borers."

Adds Mercer, "You can't get good control with chemicals unless your timing is right. It's a sick feeling when you call the aerial applicator and he says he'll be out in three days."