Bt Hybrids Compared in Pennsylvania
Greg Roth
Department of Crop and Soil Sciences
Penn State
February 1999
In numerous on-farm trials conducted around the state this year we evaluated the potential benefits of Bt corn. Extension agents in several counties conducted replicated four or six row strip tests evaluating different Bt varieties. Various seed companies cooperated by contributing seed and the use of weigh wagons.
Adams County extension agent Larry Swartz conducted an extensive evaluation of Bt hybrids on six farms. Larry's demonstrations had been featured in a previous edition of Corn Talk. Larry's data across six farms revealed no difference in yield among Bt hybrids and normal hybrids at any of the locations. At the Horst farm for example, Larry compared Dekalb 595 and Dekalb 595Bt. Yields averaged 125 bu/A for both hybrids, and there was no lodging in either hybrid. There was also no difference in grain moisture. Based on Larry's tests we would conclude corn borer pressure was low in that area this year and that there was no yield advantage to the Bt hybrids. Also, he didn't find any yield drag in the Bt products he evaluated.
In Lebanon County, extension Agent Del Voight planted two locations of a strip trial containing Bt and normal hybrids. Del found that hybrids averaged from 176 bu/A to 145 and Bt hybrids were present in the top, middle and bottom of the test. Corn borer pressure was light at both of the locations of the test.
We also conducted a replicated small plot trial in northern Lebanon County in conjunction with the agent there. In this test we had 4 non Bt hybrid and three Bt hybrids. Here we found the Bt hybrids to average 154 bushels/A and the non Bt hybrids to average 157 bushels/A- not a significant difference in yield. The Bt hybrids had no lodging and the normal hybrids averaged about 4% broken stalks, so corn borer pressure was light to moderate. We evaluated corn borer tunneling in the normal hybrids and found an average of 1.7 tunnels per plant.
We planted the same test in Lancaster County and found similar results- both the normal and Bt hybrids averaged 181 bushels per acre. There was more lodging here however, as the normal hybrids averaged about 17% lodged plants compared to almost none for the Bt hybrids. Apparently the second generation corn borers came in too late to cause severe yield losses.
We conducted another test at our research station in Landisville in conjunction with John Yocum and Lancaster Extension Agent Bob Anderson. Here we planted a Bt hybrid and its normal counterpart in late April and late May. This is the second year we have conducted this trial. In this trial we found only 3 bu/A difference among the hybrids at the early planting but a 13 bu/A advantage to the Bt hybrid in the later planting. We also found about 14 % lodging in the late planted normal hybrid and about 1% higher grain moisture in the Bt hybrid.
For silage, we had two other tests out that contained Bt hybrids and their normal counterparts. One was located in Franklin County and another in southern Lancaster County. In both there was an 1.5 to 3 T/A advantage for Bt hybrids compared to their normal counterparts. Within each trial there were other normal hybrids that did as well or better than the Bt hybrids, however.
The results of this years evaluation indicated several issues. First, corn borer pressure was generally low this year and we did not find many large advantages to the Bt hybrids for yield. It is probably safe to say that responses to Bt in our area were lower than average this year. In some cases, there were some differences for lodging and the Bt hybrids had their trademark excellent standability and corn borer control. In most cases, the Bt hybrids did not yield lower than their normal counterparts. Our data from Landisville for the past two years suggests that later planted corn may be more responsive to the Bt genetics.
In conclusion, we will continue to need to evaluate Bt hybrids to get a better handle on the economics over a range of corn borer pressure. Also, our study demonstrates the need to compare the Bt hybrids for yield just as we do with other hybrids.