What is in this article?:
- 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.
- Bt genes in a corn hybrid will not increase yield potential. Instead, the gene(s) prevent yield losses from certain insects.
- 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.
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.