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Yield Results from 1996 Bt Corn Trials

Crop and Soil Environmental News, July 1997

Charles Hagedorn
Extension Specialist, Biotechnology

This article reports on a Bt corn trial that was conducted by researchers at the University of Illinois in 1996. While Bt corn is appearing in Virginia, all Bt varieties to date are designed to control the European corn borer, which is more of a problem in the Midwest than in the Mid-Atlantic region.

In the Illinois field trial, Bt corn hybrids from five different companies (Cargill, Ciba [now Novartis], Monsanto, Mycogen, and Northrup King) were tested against their non-Bt isolines. Bt corn hybrids from Ciba and Mycogen were commercially available for planting in 1996. Northrup King's, Cargill's, and Monsanto's Bt corn hybrid became available for planting in 1997. Half of each replication of the trial was manually infested to simulate infestations by both first-and second-generation corn borers. The other half of each replication was left alone for natural infestations of corn borers to occur. No insecticides were applied for control of any insects.

The results are displayed in the accompanying table. The Bt-corn hybrids with the YieldGardTM technology from Monsanto [Cargill, Monsanto, Northrup King] protected the plants for a longer period of time during the season than did the Bt-corn hybrids from Ciba and Mycogen. Because the level of expression of the Bt endotoxin declines in Ciba's and Mycogen's hybrids after pollination, some second-generation borers may have survived and tunneled in the stalks, shanks and ears. Whether this translates into significant yield losses has yet to be determined. As expected, the percentage of non-Bt corn plants injured was considerably higher than the percentage of Bt corn plants injured. However, the yield data did not correlate well with the percentage of plants injured. Northrup King's N6800 non-Bt corn hybrid (96% of the plants injured by corn borers) was the highest yielding hybrid in the trial (134 bushels per acre). It outyielded its Bt isoline (l% of the plants injured) by 14 bushels per acre. Ciba's MAX454 Bt hybrid (34% of the plants injured) outyielded both Monsanto's Bt hybrid (6% of the plants injured) and Northrup King's Bt hybrid. Cargill's Bt hybrid (4% of the plants injured) was the best yielding Bt hybrid in the trial (128 bushels per acre).

The lack of correlation between corn borer damage and yields was due to large variability among individual plots within the trial (statistical range was 29 to 184 bushels per acre). As a result, the least significant difference (LSD) was 19.5, indicating that the mean yields were not statistically different. The wide variability at this site was attributed to unequal levels of rootworm control across the trial area. While the trial was in an area that had been planted to soybeans in 1995, appropriate soil insecticides had been used.

Regardless of the problems with this field trial, I have reported the results here because they suggest something we all should remember when gaining experience with transgenic crops. Bt corn hybrids are not a panacea for control of European corn borers; they are one more tool for management of the pest. In addition, the Bt-toxin-producing gene must be placed within hybrids that have positive agronomic characteristics if Bt hybrids are to be of any interest to growers. Although I don't know much about the tolerance of the non-Bt corn hybrids to corn borer injury in this one trial, growers should consider corn borer tolerance as a viable management option. Growers should realize that some commercially available non-Bt hybrids have relatively good levels of tolerance to corn borer injury and will produce good yields despite infestation by corn borers. Keep in mind that Bt corn technology is relatively new, so inconsistencies in research trials won't be uncommon. As the technology becomes more widely used, results should become easier to interpret. Periodic updates will be provided during the 1997 growing season.

Yield and plant injury evaluations from the Bt corn efficacy trial, University of Illinois, 1996.

Mean yield
Percentage of
plants injured
B73 x Mo17
(non-Bt corn, Monsanto)
B73 x Mo17
(Bt corn, Monsanto)
(non-Bt corn, Northrup King)
(Bt corn, Northrup King)
(non-Bt corn, Cargill)
X7570 Bt
(Bt corn Cargill)
(non-Bt corn, Mycogen)
NG 7059
(Bt corn, Mycogen)
CG 4494
(non-Bt corn, Ciba)
(Bt corn, Ciba)

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