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.

Six bushel increase

Outside of the corn borer-infested area, this trait was tested at one location. At that location, the hybrid with the Bt trait yielded 6 bushels per acre more than its non-Bt isoline. This trait slightly reduced caterpillar feeding within the ear. The amount of caterpillar damage was more than was expected for this Bt trait.

Genuity VT Triple Pro (Cry1A.105, Cry2Ab2 for above ground caterpillar pests and Cry 3Bb1 for below ground rootworm pests). Within the corn borer-infested area, hybrids with the Genuity VT Triple Pro trait yielded a median 6.5 bushels per acre more than their non-Bt isolines. The range of the differences was from -11 to 14 bushels per acre.

Outside of the corn borer-infested area, hybrids with the Genuity VT Triple Pro trait yielded a median 7.5 bushels per acre more than their non-Bt isolines. The range of the differences was from -7 to 18 bushels per acre. This trait greatly reduced caterpillar feeding within the ear. This is consistent with predicted effectiveness of this Bt trait against corn earworm.

Genuity SmartStax (Cry1A.105, Cry2Ab2, and Cry1F for above-ground caterpillar pests and Cry 3Bb1 and Cry34Ab1/Cry35Ab1 for below-ground rootworm pests). Within the corn borer-infested area, the hybrid with the Genuity SmartStax trait yielded a median 2 bushels per acre more than its non-Bt isoline. The range of the differences was from -9 to 13 bushels per acre.

Outside of the corn borer-infested area, the hybrid with the Genuity SmartStax trait yielded a median 0 bushels per acre more than their non-Bt isolines. The range of the differences was from -10 to 7 bushels per acre. This trait greatly reduced caterpillar feeding within the ear. This is consistent with predicted effectiveness of this trait against corn earworm.

Agrisure Viptera 3111 (Vip3Aa20 and Cry1Ab for above-ground caterpillar pests and mCry3A for below-ground rootworm pests). Hybrids with the Agrisure Viptera trait yielded a median of 13 bushels per acre more than their corresponding isolines with the Agrisure 3000GT trait. The range of the differences was from -5 to 23 bushels per acre.

A non-Bt isoline was not available for these two hybrid families.

Both Agrisure 300GT and Agrisure 3111 are highly effective against corn borers, so it was not necessary to separate the yield response into areas with and without corn borers.

This trait produced the greatest reduction in caterpillar feeding within the ear of all the traits tested. This is consistent with predicted effectiveness of this trait against corn earworm.

The median difference for each Bt corn trait indicated that more often than not, hybrids with a Bt corn train yielded more than hybrids without a Bt corn trait, says Flanders.

“Yield differences are most likely attributable to corn borer, corn earworm and fall armyworm infestation, but it is possible that protection against other caterpillar pests also contributed to the yield differences,” she says.

phollis@farmpress.com