Bt Corn Outperforming Standard Hybrids in UW Trials

Mike Rankin
Crops and Soils Agent
University of Wisconsin - Extension

Bt corn has now been grown extensively for the better part of a decade.  Early analysis of performance ranged from "don't leave the barn without it" to "not economically feasible for most producers."  Most would agree that in years where European corn borer pressure is heavy, the value of the Bt gene returns big dividends.   But what about when corn borer pressure is light to moderate….like most years?  After all, that technology fee needs to be recovered in these types of years as well. 

Corn performance in the UW trials 

Joe Lauer, UW Extension Corn Agronomist, has been tracking Bt corn performance relative to "standard" dent corn hybrid performance across all locations of the UW corn hybrid performance trials (see figure 1).  Until 1998, normal dent corn hybrids as a group were distributed around the trial average in a 50:50 ratio.  That is, 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 1999 and continuing through 2002 the frequency with which normal dent corn hybrids yield above the trial average has been decreasing.  In 2002 only 39 percent 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 as a group they are in the top performers less frequently than was the case five years ago.

Figure 1.  Frequency of normal dent corn and specialty hybrids yielding above the trial average in the 2002 Wisconsin Corn Hybrid Performance Trials.

Is it simply because of corn borer pressure? 

According to Dr. Lauer, there are at least two possible reasons that might explain this observation. First, the Bt trait is being incorporated into the best genetics available.  Normal dent corn hybrids are being replaced by hybrids with the Bt trait.  The Bt hybrids have finished above trial average about 61 to 83 percent of time in 2002 (depending on what other transgenic trait is "stacked" with it).  Another thought is that low, undetected European corn borer pressure exists in the trials and is reducing the performance of normal dent corn hybrids. The latter reason, although a possibility, is unlikely since the trials are scouted every 2 to 3 weeks and little corn borer damage is observed.  

Is planting Bt a "slam dunk" decision? 

Once again, keep in mind that there are excellent normal dent corn hybrids available for planting.  It is important that this group of hybrids stays competitive with transgenic counterparts.  Top yields are attainable without planting Bt hybrids, but you'll have to do some homework. 

As most producers know (I hope), part of the deal with planting Bt is to also plant a 20 percent non-Bt refuge.  A refuge is simply a block or strip of non-Bt corn that provides a source of susceptible corn borer moths that will get intimate with potential resistant moths emerging from nearby Bt fields.  This will prevent (or more correctly, delay) the buildup of a resistant population.  If every producer relies on his or her neighbor to provide a refuge, thwarting resistance simply won't happen.  Word on the street is that companies and government agencies will be policing grower fields on a random basis (based on seed purchase records).  Farm income isn't that good to absorb a monetary fine for not following the Bt refuge rules.