Whenever you buy insurance, it’s helpful to weigh the cost versus the benefit. In other words, does the inherent risk justify the premium being paid? The same should be true whenever a grower makes the decision of whether or not to plant a Bt corn hybrid.

“Bt corn is really a form of crop insurance that comes in the seed bag. The presence of one or more Bt genes in a corn hybrid will not increase yield potential. Instead, the gene(s) prevent yield losses from certain insects,” according to a recent evaluation of Bt corn hybrids conducted by researchers at Auburn University, including Kathy Flanders, Extension entomologist; Brenda Ortiz, Extension agronomist; Austin Hagan, Extension plant pathologist; and other cooperators.

The most important thing to remember, states the report, 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 “insurance.”

There are different kinds of Bt corn, depending on which Bt genes have been inserted. Some Bt genes protect against stalk borers 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.

According to the researchers, the cost of Bt technology that protects against corn borers and other caterpillars is about $3.70 per acre for older products such as YieldGard Corn Borer, Agrisure CB/LL, and Herculex I. The cost of Genuity VT Triple Pro is about $10.50 per acre. Genuity VT Triple Pro contains two genes for above-ground caterpillar resistance, in addition to protection from Western corn rootworm.

2010 field trials

In 2010, a series of field trials included Bt corn hybrids paired with their non-Bt counterparts. Two Bt corn traits were tested: Genuity VT Triple Pro and Herculex I in north Alabama fields that were heavily infested with Southwestern corn borer and/or European corn borer. Bt corn also was evaluated in central and south Alabama fields that did not have corn borers.

Corn was planted on two dates, a standard recommended planting date for the particular area, and a later planting date, approximately six weeks later. The same trials were planted at the Upper Coastal Plain Research and Extension Center in Winfield, Ala.; the Tennessee Valley Research and Extension Center in Belle Mina; and the Sand Mountain Research and Extension Center in Crossville, Ala.

Three pairs of hybrids were evaluated. One hybrid in each pair contained either the Genuity VT Triple Pro or the Herculex I Bt corn trait. The other hybrid in each pair did not contain a Bt trait but was otherwise genetically identical to its Bt counterpart. All seed was treated with clothianidin (Poncho or Acceleron) at the rate of 250 mg. active ingredient per kernel. Plots were eight rows wide by 30 feet long.

There were four replications of each corn hybrid, planted in a randomized complete block design. The first planting in Crossville was destroyed prematurely so no data is available. Stand counts and ear feeding damage were evaluated for each of the remaining locations. Stalk borer infestations were rated in Belle Mina and Crossville.

Yields were recorded for all but the second planting date in Winfield, which was severely damaged by birds and raccoons. The plots in Belle Mina were irrigated and were planted at a higher seeding rate than the other two locations. Plots in Belle Mina were sprayed with a pyrethroid insecticide at planting for cutworms.

Yields from Belle Mina, Winfield and Crossville were higher for hybrids that contained a Bt corn trait than for the same hybrid without Bt. This response was not always statistically significant. Corn planted six weeks after the standard planting date had low yields, particularly in the non-irrigated locations.

What caused the difference in yields between Bt and non-Bt hybrids? According to the researchers, the field trials in north Alabama (Belle Mina, Crossville and Winfield) received high pressure from Southwestern corn borer and moderate corn earworm pressure. Fall armyworm pressure was higher in the late-planted tests. There was no corn rootworm pressure.

Hybrids with a Bt corn trait had significantly fewer corn borers than their non-Bt counterparts. Hybrids with the Genuity VT Triple Pro trait had fewer caterpillar-damaged kernels per ear than their non-Bt counterparts. This difference was statistically significant in all locations/planting dates except for Crossville when corn was planted later than the standard planting date. The hybrid with the Herculex I trait had less ear feeding in the later planting dates. Hybrids with Bt corn traits tended to have higher stand counts than their non-Bt counterparts in the first planting date, although this difference was not significantly different.

In the later planting dates, the hybrid with the Herculex I trait tended to have higher stand counts than its non-Bt counterpart. This difference was statistically significant at Belle Mina.

Estimated economic return

Does it pay to plant Bt corn hybrids in north Alabama? Estimated economic return, above the cost of the technology, at a standard planting date ranged from $12 to $84 per acre for Genuity VT Triple Pro and $6 to $8 per acre for Herculex I. For the late planting date, estimated economic return, above the cost of the technology, ranged from $24 to $72 for Genuity VT Triple Pro and $16 to $27 for Herculex I.

The “economic return” does not include other costs of production. For example, even though the Bt technology would have apparently paid for itself at Crossville, the best yielding hybrid averaged only 19 bushels per acre, which would not have been profitable when other production costs are factored in.

Late-planted corn in the irrigated test at Belle Mina yielded much better but still may not have been profitable, depending on production costs (average yields 147 to 170 bushels per acre, depending upon the hybrid).

The Auburn researchers recommend that growers always pick hybrids with good a good agronomic fit for individual farms, and make sure the hybrid has good disease resistance.

“Always consider the yield potential of the hybrid family involved, and make sure the hybrid is adapted for planting in the Southeast. Then think about what other value-added traits are available, such as herbicide resistance or Bt corn technology.”

Results from the 2010 yield trials showed that Genuity VT Triple Pro and Herculex I would have paid off in north Alabama, where there was considerable Southwestern corn borer pressure in addition to caterpillar damage in the ears.