Choosing Bt Sweet Corn Varieties
When selecting sweet corn seed varieties this year, you may want to consider selecting some of the genetically modified Bt hybrids that have built-in resistance to different insect pests. Bt sweet corn varieties have been genetically engineered with genes from the bacterium Bacillus thuringiensis (aka “Bt”), which produce proteins that are toxic to different insect pests. In the laboratory, there have been hundreds of different insecticidal proteins identified from Bt, but only about a dozen have been successfully introduced to corn, and only a handful of those traits are available in sweet corn varieties. The insecticidal proteins or “traits” available in sweet corn fall into two different categories: the “Cry” proteins, which stands for crystalline proteins and the “Vip” proteins, which stands for vegetative insecticidal proteins. Further, when each of these traits were introduced to the corn genetics, this introduction becomes patented under a trade name used for marketing. The Cry1Ab protein was the earliest trait introduced to sweet corn, and is marketed under the trade name Agrisure CB/LL. At the time it was released, Cry1Ab provided 100% control of caterpillar pests like European corn borer and corn earworm. Since then, corn earworm has become widely resistant to this protein, though it still provides 100% control of European corn borer. The Cry1Ab protein is still available in Syngenta’s Attribute I series of seeds. Other Cry proteins that are available in sweet corn are Cry1A.105 and Cry2Ab2, which are also active against caterpillars, and Cry3Bb1, which is active against some beetles, mainly corn rootworm. Cry1A.105 and Cry2Ab2 were introduced to the corn genome at the same time, and are marketed as Yieldgard VT Pro, while Cry3Bb1 was introduced separately and is marketed as Yieldgard Rootworm. These three traits are all available together in the Seminis Performance series. Although these varieties have multiple traits targeting caterpillar pests, they do not provide effective control of corn earworm. The only Vip protein available in sweet corn is the Vip3A trait, which is marketed as Agrisure Viptera. Vip3A provides excellent control of corn earworm and other ear-feeding caterpillars, but does not control European corn borer. For that reason, the Vip3A trait is included along with the Cry1Ab trait in Syngenta’s Attribute II and Attribute Plus series to provide the full range of control of caterpillar pests. Field trials with these varieties provided 100% control of ear feeding caterpillars with no insecticide applications.
The Attribute II and Attribute Plus varieties of sweet corn are significantly more expensive than conventional varieties that do not include these Bt traits. However, if corn earworm is evading your current spray program, especially in mid-late summer when moth pressure is especially high, it may be worth trying some of these GMO varieties that offer full protection from ear-feeding pests. It is worth noting that none of the Bt traits will control stink bugs or sap beetles, so insecticide sprays may still be needed to manage these pests, though these pests can typically be managed with a single insecticide application. If you are considering buying Bt sweet corn seed this year, below is a useful table that summarizes all of the varieties that are available, the pests they control, and the herbicide tolerance included in the package. This table is also available at: https://www.texasinsects.org/bt-corn-trait-table.html.