Bt hybrids saved lots of corn yield in 1997, a year of heavy European corn borer pressure. They also showed an edge in 1998 and promised the same in 1999, years of much lighter pressure.

"They do what they say they will do - give excellent protection against corn borers," says Mark Kottmeyer, a Kearney, NE, crop consultant. "Hybrids with the YieldGard event protect against both first and second generations, while some of the other Bt events give good protection through pollination."

Monsanto reports that hybrids with its YieldGard technology yielded considerably better than non-Bt hybrids across the Corn Belt in 1997. The yield advantages were 17.4 bu/acre in Illinois, 12.9 in the Dakotas, 12.2 in Iowa, 12 in Kansas and 10.5 in Nebraska.

For 1998, Bt yields were higher by 1.5 bu/acre in Illinois, 7.7 in the Dakotas, 3.1 in Iowa, 3.7 in Kansas and 4.2 in Nebraska.

The average yield in 1998 Iowa State University trials was 162.6 bu/acre for Bt hybrids vs. 159.7 for the same hybrids without the Bt gene.

Although corn borer pressure was generally light again in 1999, there was damage in many areas. Agronomists and crop consultants expected Bt hybrids to show a yield advantage.

"We had a 10-20% infestation of first-generation borers," notes crop consultant Shannon Gomes, Waverly, IA. "I would estimate a 5- to 10-bu yield advantage for Bthybrids in those cases.

"Later in the season we had earworm, but the Bt hybrids with YieldGard protection seemed to suffer less damage than non-Bt corn," Gomes adds.

Gomes sees better plant health with Bt hybrids, even when borer pressure is moderate.

"There is more 'stay green' because of less disease entering the plants where borers have penetrated," he points out. "Standability is better and the ears are better formed."

Farmers generally have been hesitant to spray for corn borers, Gomes says, especially for the second generation.

"By that time of the year they have spent all they want to spend on the crop and don't want to shell out another $15 per acre. Now they can get the sure protection of Bt corn for about $10 per acre," he says.

Planting Bt corn is a long-term investment, not a short-sighted tactic to be used or not used depending on the borer population the year before, says University of Illinois entomologist Kevin Steffey. There isn't much correlation between corn borer densities from one year to the next, he says.