Bt corn has entered the marketplace in full swing for 1997. There will be numerous Bt corn hybrids with several different genetic Bt events that provide different levels of protection against the European corn borer. Many have requested performance data from Iowa State University, but last year we had limited amounts of seed and only had two tests at one location. Because our data set was small, I gathered results from entomologists at other land-grant universities in the Corn Belt. This information should be beneficial in helping you gain a better understanding of Bt corn performance across a large geographical area under variable corn borer populations.
Before we get to the results, let's briefly review the status of Bt corn. As of today, there is only one Bt gene that occurs in any commercial corn hybrid. This Bt gene is called Cry1Ab (pronounced cry-one-A-bee). However, this gene has been modified in the laboratory three different ways into what are known as events 176, Bt-11, and MON-810 (an event is the process of modifying the gene and inserting it into plant cells).
Bt event 176 is the gene modification used by Ciba Seeds/Novartis and Mycogen. This event has been trademarked by Ciba Seeds/Novartis as KnockOut and they placed it in their Maximizer line of hybrids. Mycogen has trademarked the same event 176 as NatureGard for their Bt hybrids.
Bt-11 is the genetic event developed by Northrup King/Novartis. This genetic material was provided by Monsanto and is trademarked as YieldGard technology in the NK/Novartis hybrids.
Monsanto has developed a different event, MON-810, and it will appear in Cargill, DeKalb, Golden Harvest, and Pioneer hybrids for 1997, also under the YieldGard trademark.
So here's what we have: one gene (Cry1Ab), three genetic events (176, Bt-11, MON-810), with event 176 under two trademarks (KnockOut and NatureGard) and events Bt-11 and MON-810 under one trademark (YieldGard). Believe me, it will only get more confusing in the future when additional genes get added to the hybrids!
Data are presented from university trials in six states:
All plots had natural populations of European corn borers, but some of these populations were supplemented with laboratory-reared eggs or larvae to create an "artificial" population. The purpose of the artificial population is to assure that all plants are attacked by corn borers. The Kansas State trials also had a natural infestation of southwestern corn borer; this is an insect that does not occur in Iowa. No insecticides were applied to any of the plots. Two measurements are provided in each test: stalk tunnels (measured in inches per plant or number per plant) and grain yield (bushels per acre). Statistical analyses were provided in some, but not all tests.
What can we learn from this information?
First, all Bt genetic events do not provide equal control. Hybrids with the YieldGard technology provide season-long control of European corn borers. Stalk injury was zero in most YieldGard hybrids and never exceeded 0.2 inch of tunnel. The Ciba and Mycogen hybrids often had some stalk injury, although it was much less than the non-Bt hybrids. The difference in the performance is that the YieldGard events produce the Bt endotoxin (this is what kills the corn borer larvae) at high levels throughout the season, whereas the event 176 (KnockOut and NatureGard) does not produce large enough concentrations of the Bt endotoxin late in the season. This allows some second generation European corn borers to survive and tunnel into the stalk.
Second, a Bt hybrid may not necessarily produce the highest yields. Several of the tests had non-Bt hybrids that yielded just as much or more than competitive Bt hybrids, even under corn borer pressure. The insertion of a Bt gene into a plant may make it a better hybrid, but not necessarily the best yielding hybrid. The Bt gene only provides yield protection, not a yield increase. This is a very common misunderstanding. Remember that yield is a function of many genes within the plant plus the influence of environmental and agronomic factors.
Third, more Bt hybrid data are needed. We have the most information on the Ciba Maximizer hybrids; you should be able to make the most informed decisions about their use. Several companies will sell Bt corn in 1997 but they did not have hybrids in any university trial last year. The performance of these Bt hybrids needs to be included in future evaluations.
Fourth, Bt corn is just one tool for managing the European corn borer. It will not eliminate the European corn borer as a pest. But, it does offer the safest, most economical, environmentally friendly method of managing a serious pest of corn. The final determination is yours. Evaluate it on your farm and determine if Bt corn provides the European corn borer control and grain yields you expect.
This article originally appeared on pages 15-17 of the IC-478 (2) -- March 3, 1997 issue.