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Issue No. 2, Article 2/April 6, 2012

Bt Use and Refuge Implementation: Expected Patterns for 2012

The use of Bt hybrids by Illinois producers remained strong in 2011. On average, 95% 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% (Quincy, 43 total participants) to near 97% (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.

Figure 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% of producers across the seven locations (627 total participants) indicated they had established a refuge according to current recommendations. Compliance ranged from 77% of 105 (Bloomington) to 91% 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.

Figure 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% 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% 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% structured refuge by producers over requirements tailored to the unique biological characteristics of corn rootworms.

Today's producers have much greater flexibility with respect to the type of refuge they wish to implement. We asked producers at the 2012 Classics what type of refuge they intended to use this growing season. The 20% structured refuge was most common (53%; Figure 3), but the seed blend (refuge-in-a-bag) strategy is gaining popularity as more pyramided Bt hybrids enter the marketplace. About 22% of producers indicated they would use a 5% seed blend this season, and slightly more than 14% intend to use a 10% seed blend. Combined, nearly 37% of producers who took part in the 2012 Classics will use a seed blend as their refuge and hedge against insect resistance development.

Figure 3. Answers provided at the 2012 Corn and Soybean Classics meetings to the question "Which of the following describes your refuge approach for 2012?"

This is a very significant shift away from the structured refuge, and the trend will likely intensify as more pyramided hybrids become available. From a convenience angle, it's easy to see why this approach will increase in popularity. Of potential concern is the anticipated reduction in the volume of non-Bt seed produced by the seed industry, since refuge requirements are dropping from 20% levels. Will this make it more difficult for producers to purchase elite germplasm from non-Bt product lines? Producer access to non-Bt hybrids is important if the industry overall values a more integrated approach to pest management across the Corn Belt.--Mike Gray

Mike Gray

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