| Low commodity prices and environmental concerns compel cotton growers to increase production efficiency and decrease inputs. Research evaluated weed interference, no-tillage production, transgenic cultivars, and new herbicides to improve weed management in cotton. Relationships between weed density and cotton yield loss were explained by hyperbolic functions for four weeds. Estimated I values (yield loss per unit density as density approaches zero) were 36 to 14, 52 to 40, 29 to 23, and 43% for ladysthumb, Pennsylvania smartweed, pale smartweed, and tropic croton, respectively. Increasing weed biomass resulted in decreased cotton yield in all cases. Large amounts of late-season smartweed biomass were produced, but competitiveness was similar to that of small weed species due to slow early-season weed growth. Smartweed spp. produced between 18,000 to 63,000 achenes m-2 at 1 weed per m-1 cotton row underscoring concerns of economic threshold management strategies. Studies evaluated weed management programs in non-transgenic, bromoxynil-resistant, and glyphosate-resistant cotton in no-tillage and conventional-tillage environments. Tillage did not affect weed control, but conventionally tilled cotton yielded 17% more than no-tillage cotton. Excellent (>90%) velvetleaf, common lambsquarters, jimsonweed, morningglory, and prickly sida control was achieved with pyrithiobac, bromoxynil, and glyphosate programs. Net returns from glyphosate programs were as high or higher than net returns from programs utilizing mid-season bromoxynil, pyrithiobac, or fluometuron plus MSMA treatments. In separate experiments, nine flumioxazin applications (36 or 70 g ai/ha) between 0 and 10 weeks prior to cotton planting and applications to 15- or 30-cm tall cotton indicate cotton tolerance. Flumioxazin postemergence-directed (70 g ai/ha) applied alone or with glyphosate or MSMA controlled a large spectrum of broadleaf weeds four wk after treatment. Cotton yield was not affected by flumioxazin treatments compared to commercial standards and nontreated controls, indicating its potential use in weed management strategies. Uptake, translocation, and metabolism studies of 14C-CGA 362622 foliar applied to cotton, peanut, jimsonweed, and sicklepod indicated that differential tolerance between species was due to differences in metabolism and absorption. CGA 362622 was rapidly converted to more polar metabolites by cotton and jimsonweed while sicklepod and peanut metabolized the herbicide more slowly. |
