Reduced-input, postemergence weed control with glyphosate and residual herbicides in second-generation glyphosate-resistant cotton.

摘要

Field studies were conducted in 2004 and 2005 to evaluate weed control following post-emergence (POST) applications of glyphosate in combination with either S-metolachlor (premix formulation), pyrithiobac, or trifloxysulfuron in conjunction with glyphosate in second-generation glyphosate-resistant cotton (Roundup Ready Flex). These herbicides were applied in combination with glyphosate in a two-application programme at the 2-leaf (LF) (followed by glyphosate alone at the 10-LF growth stage), 6-LF (following glyphosate alone at the 2-LF growth stage), or 10-LF (following glyphosate alone at the 2-LF growth stage) cotton growth stages. No differences in weed control between residual herbicide were observed for goosegrass (Eleusine indica), hemp sesbania (Sesbania exaltata), Johnsongrass (Sorghum halepense), Palmer amaranth (Amaranthus palmeri), redroot pigweed (Amaranthus retroflexus), sicklepod (Cassia obtusifolia), or smellmelon. The optimum control of barnyardgrass (Echinochloa crus-galli) and browntop millet (Brachiaria ramosa) was achieved with glyphosate plus S-metolachlor. No differences were observed among the application timings for control of goosegrass, hemp sesbania, Johnsongrass, pitted morningglory (Ipomoea lacunosa), and smellmelon. The control of barnyardgrass, browntop millet, Palmer amaranth, redroot pigweed, and sicklepod was optimized with residual herbicide application at the 2- or 10-LF timing. No yield differences were observed between the residual herbicides, and seed cotton yield averaged 2800 kg/ha. The yield was maximized when the residual herbicide was applied at the 2- or 10-LF growth stage (2960-2730 kg/ha). Analysis based on numerical yield at particular residual-herbicide application timings and calculated yield for each timing based on the percentage of a standard three-application glyphosate programme indicated the most consistent residual-herbicide timing for optimizing yield in a reduced-input Roundup Ready Flex weed-control programme occurred at the two-leaf growth stage. All the reduced-input programmes, however, resulted in cotton yield of at least 93% of that obtained with the standard programme.