During the 1996 growing season, Bt corn was first introduced but was planted to a very small number of acres due to limited supplies of seed. Projections are for the number of acres to rapidly increase as more seed becomes available and as seed companies rush to add the various Bt mechanisms to their hybrids. Some seven million acres were planted to Bt corn in 1997 with hybrids primarily from Mycogen, Novartis (formerly Ciba), and Northrup King. This past winter, Bt corn has been on the agenda at most grower meetings as producers want to know how well the Bt hybrids have worked and whether or not there are any problems or disadvantages they should know about. This article summarizes comments from several grower and commodity meetings and focuses on the use and expansion of Bt corn in the Southeast. The optimism about the future of Bt corn is because some of the Bt lines growers can expect to see in the future are very specific for corn earworm and fall armyworm, serious economic corn pests in the Southeast.
The overall consensus is that Bt corn will not be an immediate fit in most Southeast cropping systems, but the future of Bt corn appears promising. There are several reasons for this conclusion, but the main one is that most of the technology and research has been conducted in the major corn-producing areas of the Midwest, and all of the initial lines of the Bt hybrids have targeted European corn borers (ECB), a major insect pest of the Midwest. The ECB is generally not an economic problem on corn in the Southeast, although it can be, particularly on late-planted corn. The current Bt lines are not effective on corn earworms, fall armyworms, any of the root pests and other insects pests like stink bugs, that are problems on Southeast corn.
Several other conclusions were developed at grower meetings around the Southeast, and these are summarized as follows:
1) Growers should evaluate Bt corn primarily on a trial basis and realize that this technology is in its infancy in Southeast corn production. At present there is not a large enough research and educational base in the Southeast to know what kind of influence Bt corn lines will have on other cropping systems, such as Bt cotton.
2) Corn can be produced fairly successfully throughout the Southeast without too much concern over insects because the primary recommendation for controlling insects in corn in the Southeast is to plant early, and use at-planting insecticides where and when needed. This approach reduces the need for Bt hybrids at present, as long as the only insect control available with the Bt lines is for ECB.
3) An education program will be needed because growers will always have to keep in mind that the Bt gene expresses itself in the corn plant in different ways, and there are also are different Bt genes that have been placed into different corn lines. All Bts are not the same and the different Bt genes are equivalent to different insecticides.. Some of the Bts are expressed only in the leaves, some are expressed in the silks, some in the kernels and some even in the roots. Some will express themselves in very young tissue but, as the plant matures, the expression is diluted. With so many Bts becoming available, growers will be challenged to be sure they have selected the Bt line that is most appropriate for their production system and their specific insect problems.
4) In trials conducted this past year with the first generation of Bt corn lines, yields were very similar to non-Bt varieties. However, significant yield differences have been seen in some of the newer Bt varieties. Growers should not sacrifice yields just to use the new Bt lines. There will also be a technology fee $15 to $18 per bag and the issue of non-Bt "refugia" is still not completely resolved..
5) Until this year, it has been illegal to plant a Bt corn line in the Southeast in those areas where cotton is grown. The EPA has, to date, restricted the corn Bt technology to those areas where cotton is not grown. While nothing official has been released form EPA, the "unofficial" information being provided to growers indicates that all of the Bt corn varieties will be available for planting in cotton producing areas of the Southeast in 1998. Apparently, EPA will waive the initial restriction and will limit the amount of acreage planted to Bt corn to about five percent of the total acreage where 1,000 acres or more of cotton are grown. This type of ratio will have to be worked into Southeast production systems so that use of Bt corn does not hurt Bt cotton programs through the development of Bt-resistant pests. The use of this type of ratio approach will be reviewed and modified by EPA as experience develops over the next few years when data becomes available on Bt corn in areas that are also planted to Bt cotton.
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