Expected patterns of Bt use, implementation

The use of Bt hybrids by Illinois producers remained strong in 2011. On average, 95 percent of producers participating in the regional January 2012 Corn and Soybean Classics (639 total participants) indicated they planted a Bt hybrid in 2011 (Figure 1). Use ranged from 86 percent (Quincy, 43 total participants) to near 97 percent (Bloomington, Moline, Mt. Vernon, and Springfield). This very high rate has been common across Illinois for several years despite low numbers of key insect pests such as the European corn borer and the western corn rootworm.

click image to zoomFigure 1. Answers provided at the 2012 Corn and Soybean Classics meetings to the question "Did you plant a Bt hybrid in 2011?" Intense use of Bt hybrids is also anticipated for the current growing season. On numerous occasions, I have questioned the wisdom of applying such intense selection pressure on insect populations when many pest species are well below economic levels in most producers' fields. Nonetheless, the pattern is not expected to change.

At the 2012 Classics, producers also were asked if they planted a refuge in 2011 according to suggested guidelines (Figure 2). On average, 83 percent of producers across the seven locations (627 total participants) indicated they had established a refuge according to current recommendations. Compliance ranged from 77 percent of 105 (Bloomington) to 91 percent of 105 (Champaign). The proper establishment of refuges will become increasingly important as more acres are planted to Bt hybrids, selection pressure increases, and the threat of western corn rootworm resistance development looms.

click image to zoomFigure 2. Answers provided at the 2012 Corn and Soybean Classics meetings to the question "If you planted a Bt hybrid in 2011, did you plant a refuge according to the suggested guidelines?" When Bt hybrids entered the marketplace in 1996 and for many years after, use of a 20 percent refuge was standard protocol for the Corn Belt. This guideline was based on the use of Bt hybrids aimed primarily at the European corn borer that expressed a high dosage level of Cry proteins. In 2003, Bt hybrids were commercialized for corn rootworms, and similar 20 percent structured refuge requirements were implemented across the Midwest.

The Bt hybrids targeted at corn rootworms were not high dose, and the mating characteristics along with dispersal patterns differ strikingly between corn rootworms and European corn borers. So why the similar refuge requirements? The reason was primarily related to familiarity, convenience, and the presumption of more likely implementation of the 20 percent structured refuge by producers over requirements tailored to the unique biological characteristics of corn rootworms.