To Bt or Not to Bt in 2000

November 5, 1999
We're paraphrasing a title of a presentation we made at the Agronomy Day at the University of Illinois South Farm in 1998, but it seems appropriate now as growers contemplate their planting plans for 2000. We know that growers select corn hybrids based on many factors, but until recently, insect resistance was not central among those factors. However, with the advent of Bt corn for control of European corn borers, all that changed. Growers now consider the questions, "Should I plant Bt corn?" and "How much Bt corn should I plant?" when they mull over their choices of corn hybrids.

Since 1996, when the first Bt-corn hybrids became available, we have indicated that Bt corn was a tool for management of European corn borer (and southwestern corn borer in southern counties), not a silver bullet, and not for everybody every year. In fact, we have provided some historical data about the frequency of economic infestations of corn borers in different areas of the state to help people make more informed decisions about Bt corn. So as the time to purchase seed for 2000 draws near, let's ponder some of the questions and answers associated with considerations of Bt corn.

Will Bt corn offer an economic return on my investment in 2000? The answer to this question has become more complicated within the past year. We have always stated that in years when corn borer infestations are not economic, a grower who has planted Bt corn cannot expect a return on his or her investment in the premium paid for the seed. Most people realize that the densities of European corn borers have been quite low during the past two years (1998 and 1999), and so returns on investment have been few and far between.

Complicating the assessment of the need for Bt corn are the low commodity prices and the current issues associated with the use of any genetically modified (GM) crop (more on this later). The low value of corn right now and the lack of economic infestations in 1998 and 1999 probably have led some growers to question the need for paying a premium for Bt corn in 2000.

The decision to use Bt corn as an economically viable management tool depends on a grower's experience with European corn borer populations over time. In areas where corn borers cause economic damage frequently (for example, 6 or more years in 10), Bt corn may pay dividends in yield protection. However, in areas where economic infestations of corn borers are infrequent (for example, 1 to 3 years in 10), a grower who pays the premium for Bt corn every year probably is not making a wise decision. In those areas, a strategy of scouting and treating with an insecticide only when necessary is a more reasonable choice. The accompanying article about the results of our 1999 fall survey of European corn borers might shed some additional light on the subject.

Will the issues associated with GM crops go away so I can plant them in peace in 2000? The answer to this question is not known for certain, but in the short term, the answer probably is "no." The public debate about the use of GM crops, including Bt corn, will continue for a while. Therefore, the issues will continue to have an impact on growers' decisions about using Bt corn.

The main public issues associated with Bt corn have focused on its potential impact on nontarget insects (specifically monarch butterflies; refer to the accompanying article) and the segregation of GM grain from non-GM grain for purposes of export. These issues have almost overshadowed the original issue regarding the potential for European corn borers to develop resistance to the Bt endotoxin. However, regardless of your take on the issues, the fuss will continue. Therefore, as growers consider their choices of corn hybrids for planting in 2000, they must consider the impact of segregating grain on their bottom line. If some elevators continue to pay premium prices for non-GM grain, the decision to grow non-GM grain might make reasonable economic sense to some growers. Transportation costs for hauling grain to selected elevators also need to be considered.

Okay, so I've considered the economics and issues associated with Bt corn, and I'm going to plant it anyway. Do I still need to be concerned about insect resistance? The answer to this question is an emphatic "yes." Despite all of the other issues, the potential for European corn borers to develop resistance to the Bt endotoxin looms among the most important considera- tions. The consensus among university entomologists, industry scientists, and the National Corn Growers Association is that a 20 percent non-Bt-corn refuge must accompany all plantings of Bt corn. In addition, the non-Bt-corn refuge must be adjacent to or within a field of Bt corn. Obviously this eliminates the possibility of segregating the non-Bt corn from the Bt corn, especially with an in-field refuge. However, we feel very strongly about the need to plant a non-Bt-corn refuge for insect resistance management. Therefore, if you plant an in-field refuge, you have to consider it as GM grain when you market it after harvest.

The next millennium is going to be exciting for all of us involved with agriculture. Who knows what issues regarding GM crops will arise in 2000? Who knows what issues regarding anything in agriculture will arise in 2000 or beyond? All we can suggest is that you be prepared for almost anything.--Kevin Steffey and Mike Gray

Author: Kevin Steffey Mike Gray