Trials conducted this past summer in Alabama reinforced the notion that Bt corn hybrids should be considered a form of crop insurance for Southeastern growers who already have or who anticipate insect pressure.

The presence of one or more Bt genes in a corn hybrid will not increase yield potential, says Kathy Flanders, Auburn University Extension entomologist.

“Instead, the gene(s) prevent yield losses from certain insects. Therefore, the most important thing to remember is that if the population of the target insect in your field or area is high enough, Bt corn will pay off.

“If the insect pressure is not there, then you won’t get your money back. So it is a matter of deciding if the risk is high enough to warrant purchasing this ‘insurance.’”

Some Bt genes protect against stalk borers, explains Flanders, and others help prevent leaf and ear damage from various caterpillars including corn earworm and fall armyworm.

Still other genes protect the roots from Western corn rootworm. These genes are bundled together in various combinations, with or without herbicide tolerance genes.

In the Alabama trials, six Bt corn traits were tested: YieldGard Corn Borer or Agrisure 3000GT or Genuity VT Triple, Herculex I, Optimum Intrasect, Genuity VT Triple PRO, Genuity SmartStax and Agrisure Viptera 3111.

The following is a summary of each trait’s performance:

Herculex I (Cry1F protein). Within the corn borer-infested area, hybrids with the Herculex I trait yielded a median 11 bushels per acre more than their non-Bt isolines. The range of the difference was from 6 to 34 bushels per acre.

Outside the corn borer-infested area, hybrids with the Herculex I trait yielded a median 4 bushels per acre more than their non-Bt isolines. The range of the differences was from -16 bushels per acre to 28 bushels per acre.

This trait slightly reduced caterpillar feeding within the ear. This is consistent with predicted effectiveness of this Bt trait against corn earworm.

Optimum Intrasect (Cry 1Ab and Cry1F proteins). Within the corn borer-infested area, the hybrid with the Optimum Intrasect trait yielded a median 16.5 bushels per acre more than its non-Bt isoline. The range of the difference was from 11 to 22 bushels per acre.