Weed control and economic evaluation in glyphosate-, glufosinate-, glyphosate acetyltransferase-resistant, and conventional soybean

Soybean weed management is a perennial challenge, and evaluation of new cultivar programs is essential to allow producers to decide which programs fit their needs. The objective of this study was to determine weed control, crop tolerance, yield, and gross revenue less weed control cost (GRLWC) from four soybean cultivar programs [glyphosate-resistant (RR), glufosinate-resistant (LL), glyphosate acetyltransferase-resistant (GAT), and conventional (CON)]. Research was conducted in 2009 and 2010 at Keiser and Pine Tree, AR, in a split-split-plot design with two planting dates [early planting date: late April to early May (maturity group IV); late planting date: early June (maturity group V)] as the whole-plot factor, four cultivar programs as the subplot factor, and six herbicide programs (weedy check; delayed preplant burndown (PPB) followed by (fb) postemergence (POST); preemergence (PRE) or POST alone; short-residual preemergence (SPRE) fb POST; long-residual preemergence (LPRE) fb POST; and POST fb POST) as the sub-subplot factor. GRLWC was compiled by adding all weed control costs (chemical cost, application cost, and technology fee if applicable) and subtracting from the gross revenue (yield multiplied by the cash sale price from the nearest elevator on the day of harvest). Soybean injury was visually negligible among the cultivar programs. All herbicide programs produced higher GRLWC and yields than the untreated check. Herbicide programs with multiple herbicide applications were superior to programs with a single herbicide application in terms of weed control, yield, and GRLWC. The RR and LL SPRE fb POST (flumioxazin fb glyphosate or flumioxazin fb glufosinate, respectively) were comparable in terms of the highest GRLWC and yield in any location by planting date combination. All four cultivar programs had a herbicide program that effectively controlled the weed spectrum throughout the growing season. In conclusion, considerations such as soybean cultivar yield potential, variability in price, location, and herbicide application timing should be considered when deciding which cultivar program and herbicide program to choose.