Callaway County
Callaway County
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Jarman's Weekly Agronomy News January 12, 2000 |
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Yield Comparisons of Bt and Non-Bt Corn Hybrids in Missouri in '99 |
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Full-season corn hybrids were evaluated in nine non-irrigated and six irrigated trials in the University of Missouri Variety Testing Program in 1999. Seed corn companies had two options for assessing the performance of Bt hybrids. There were fifteen standard corn hybrid trials averaging 75 hybrid entries per trial or separate smaller Bt corn trials. These smaller trials were comprised of eight non-irrigated Bt corn hybrids and four irrigated Bt corn hybrid trials grown against three productive non-Bt hybrids selected on the basis of high yield performance in the MU Variety Testing. In three of the 15 separate Bt trials, the non-Bt hybrids were artificially infested with European corn borer. The objectives of this trial were to evaluate yield performance of Bt and non-Bt corn hybrids under natural European corn borer infestation and the yield performance of non-Bt corn hybrids under two levels of artificial European corn borer infestation. Natural levels of first and second-generation European corn borer infestations were monitored. Then, the economic benefits of the Bt technology were assessed to determine the level of European corn borer infestation that offsets the higher seed cost of Bt corn seed. Natural infestation levels of European corn borer were low at the 15 trial locations, ranging from fewer than 10% tunneled plants at six trial locations to 37% tunneled plants at the non-irrigated Columbia and Chillicothe trials. When yield comparisons were made between the top 10 Bt and non-Bt hybrids, the level of natural infestation did not appear to have a consistent effect on the yield performance. When yield comparisons were averaged over the standard trials, the top 10 Bt hybrids and top 10 non-Bt hybrids were within 1.0 Bu/A of each other. On a regional basis, there were larger differences in yield performance when the Bt and non-Bt hybrids were compared in the four irrigated trials in the southern half of the state. Overall, the Bt hybrids yielded higher in the southwestern Missouri trials and lower in the southeastern Missouri trials than the non-Bt hybrids. Yield comparisons in separate Bt trials closely followed those obtained in the standard trials, with the exception of the irrigated trials in southeast Missouri. The three top-yielding Bt hybrids yielded only 3.0 Bu/A more than the three non-Bt hybrids when the yields of the two "Bootheel" trials were averaged. There was no "yield drag" or "yield lag" associated with the performance of Bt hybrids in the 15 standard trials. The Bt hybrids comprised 42% of the hybrids that were the highest yielding or that did not yield significantly less than the top performer. The Bt hybrids accounted for 40% of all hybrids that yielded above the average. The artificially infested non-Bt hybrids averaged 100% infestation with an average of 5.2 tunnels per plant and a mean tunnel length of 9.5 inches. In comparison, only 34% of those cornstalks from the naturally infested non-Bt hybrids were tunneled, with an average of 1/2 tunnels per plant and a mean tunnel length of 3/4 of an inch per plant. In the naturally infested non-Bt hybrid plots, approximately 70% of the tunnels were initiated after the tassel stage by second or third generation corn borers. In the artificially infested non-Bt hybrid plots, over 95% of the stalk tunneling began at the blister stage, approximately one week after the artificial infestation. The stage of growth when tunneling begins can have a big difference on yield reduction. In this case 2 bushels per acre or 1.5% yield reduction from the earlier infestation based on equal infestations per borer per plant. It is clear that there is a return on the Bt corn seed premium or technology fee when most non-Bt hybrids are heavily infested with European corn borer. However, what level of European corn borer infestation offsets the higher seed costs associated with Bt corn? Assuming the infestation began at the blister stage, the economic injury level would be one larva (tunnel) per plant based on an expected yield of 140 Bu/A, a market price of $2.00/Bu, and a technology fee of $8.50/A. The break-even point would be one larva per plant, and yield protection in excess of 4.2 Bu/A would provide a net return on the Bt technology. This report is based on Missouri corn performance trials. The complete information is available at the Callaway County Extension Center from the 1999 Missouri (Corn) Crop Performance. University of Missouri-Columbia Special Report 521, by H.C. Minor, C.G. Morris, H.L. Mason, D.R. Knerr, R.W. Hasty, G.K. Stafford, and T.G. Fritts. The performance trials are also available at http://agebb.missouri.edu.cropperf/corn/. The full 10-page Bt corn report is available from Maureen O’Day at odaym@missouri.edu. (Harry Minor, 573-882-2001 and Maureen O’Day, 573-882-3786). Missouri crop performance trial information is also available on soybeans, grain sorghum, and white corn varieties.
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