Do Cotton Varieties with Various Transgenic Traits Need to be Evaluated in Separate Trials Using Different Herbicide Programs?

Many new cultivars are now offered for sale with fewer years of public testing than most growers, consultants, and university personnel need for proper evaluation.  Proper field testing of varieties will become even more important during the next few years with the development and release of numerous new Roundup Ready Flex, Widestrike, Glytol, Liberty-Link, Widestrike 3, Dicamba, Enlist and Bollgard II varieties.  New cotton varieties are currently tested in South Carolina by Clemson University personnel in what are referred to as Official Variety Trials (OVTs).  The primary objective of these trials is to give growers and unbiased, side-by-side comparison of varieties offered for sale in South Carolina by evaluating these varieties for maximum genetic yield potential and fiber quality.  One issue that continually arises with OVT testing from the cotton community is that these varieties should be evaluated under similar management system that they will be grown in commercially (ie. conducting trials using various herbicide and/or insecticide systems, etc.).  However, incorporating various management systems into OVT trials greatly reduces the number of varieties that can be compared side-by-side and eliminates direct comparisons of varieties.   Many university researchers feel that as long as OVTs are maintained weed-free, there is no difference in the genetic yield potential of transgenic varieties sprayed or not sprayed with glyphosate or glufosinate.  The objectives of this study are to  evaluate the lint yield and fiber quality response of transgenic cotton varieties when grown under various herbicide management systems, and to determine if cotton varieties released in the near future need to be evaluated in separate trials using different herbicide programs.