1. Agricultural Research Service, U.S. Department of Agriculture, University of Minnesota, 1991 Upper Buford Circle, St. Paul, Minnesota 55108; BASF Corporation, 26 Davis Drive, P.O. Box 13528, Research Triangle Park, North Carolina 27709-3528; Bayer CropScience, 17745 South Metcalf Avenue, Stilwell, Kansas 66085; and DuPont Crop Protection, Stine-Haskell Research Center, Newark, Delaware 19714