According to Joe Lauer, UW-Extension Corn Agronomist, a recent trend in the UW Corn Performance trials is the lower frequency of normal dent corn hybrids yielding above the trial average.  From 1973 to 1996, normal dent corn hybrids as a group were distributed around the trial average in a 50:50 ratio; in other words 50 percent of the normal dent corn hybrids were above the trial average and 50 percent of the hybrids were below the trial average. 

        Beginning in 1997 and continuing through 2005, the frequency with which normal dent corn hybrids yield above the trial average has been decreasing.  In 2005 only 34% of the normal dent corn hybrids yielded above the trial average. There are still quite a few normal dent corn hybrids that have excellent performance and are the top hybrids in a trial, but greater care must be used when selecting normal hybrids. 

        There are at least two possible reasons that might explain this observation.  First, the Bt and other transgenic traits are being incorporated into the best genetics available.  Normal dent corn hybrids are being replaced by hybrids with transgenic traits.  However, it should be pointed out that there is variation among transgenic traits for performance above and below the trial average.  For example, the hybrids containing the Mon810 Bt event finish above the trial average 64 percent of the time.  Conversely, hybrids containing Mon863 often finish below the trial average.  Another possible reason for greater than expected performance of certain Bt hybrids is that low undetected European Corn Borer pressure may exist in the trials and is reducing the performance of normal dent corn hybrids. 

            It is important that the industry maintain a strong genetic base of normal dent corn hybrids because these will always be needed to plant the 20 percent corn refuge area required by EPA when growing a transgenic hybrid.