Cotton (Gossypium hirsutumL. ‘Stoneville 213’) was grown with densities of sicklepod (Cassia obtusifoliaL.) or redroot pigweed (Amaranthus retroflexusL.) ranging from 0 to 32 weeds/15 m of row. Regression of seed cotton yields on weed density revealed a linear decrease in yield with increasing weed densities. In the 3 yr these studies were conducted, losses in hand harvested yields of seed cotton ranged from 34 to 43 kg/ha for each sickledpod plant/15 m of row and 21 to 38 kg/ha for each redroot pigweed plant per 15 m of row. Under comparable weed densities, yields of seed cotton differed only slightly when hand harvested or mechanically harvested. Mechanical harvesting efficiencies of cotton were reduced only at higher densities of weeds. The percentage of trash in cotton generally increased with increasing density of weeds. Neither sicklepod nor redroot pigweed affected cotton grade or micronaire.

To determine the competitiveness of common cocklebur (Xanthium pensylvanicumWallr.) with cotton (Gossypium hirsutumL. 'Stoneville 213′), experiments were conducted on a Lucedale fine sandy loam from 1978 through 1980. Common cocklebur dry weight increased with increasing density up to 16 plants/15 m of row. No further increase in dry matter occurred beyond this density. Regression analysis showed that common cocklebur produced an average of 342 kg/ha of dry weight for each plant per 15-m row. Seed-cotton yields decreased as weed density increased up to 16 common cocklebur plants/15 m of row. Regression equations revealed yield losses ranging from 72 to 115 kg/ha for hand-harvested seed cotton and 57 to 90 kg/ha for machine-harvested seed cotton for each common cocklebur plant/15 m of row. Cotton stem diameter and height were reduced by weed competition in the same manner as seed cotton yields, but reductions were not as pronounced, indicating that these parameters were not good indicators of common cocklebur competition.

Field studies were conducted in 1996, 1998, 1999, and 2000 to determine the effect of glyphosate (isopropyl amine salt) on rice injury and yield when applied postemergence at 0, 70, 140, and 280 g ai/ha to dry-seeded rice in the three- to four-leaf (3- to 4-L), midtiller (MT), panicle initiation (PI), and boot (BT) growth stages. Glyphosate at 140 and 280 g ai/ha applied at the 3- to 4-L, MT, and PI growth stages resulted in the greatest foliar injury, and 280 g ai/ha was more injurious than 140 g ai/ha at the first rating, with the exception of MT and PI 2000, where they were equal. Glyphosate treatments resulted in the least visible foliar injury when applied at the BT stage. Rough rice yield was reduced by glyphosate applied at 280 g/ha to rice in the MT growth stage three out of four years. Applied to rice at PI, glyphosate at 140 g/ha reduced yields two out of four years, and three out of four years when applied at 280 g/ha. BT-stage applications of glyphosate at 70, 140, and 280 g/ha reduced yields two out of four, three out of four, and four out of four years, respectively.

Cotton response to triclopyr was evaluated when it was applied over-the-top at simulated drift rates to pin-head square and early bloom cotton growth stages in 1987 and 1988. The herbicidal effects of triclopyr were most evident after a lag period of 10 to 15 d. Triclopyr at 60 g ai ha-1applied at pin-head square reduced cotton height in 1987, but not in 1988. Triclopyr applied at pin-head square and early bloom reduced cotton flowering initially, as measured by white bloom counts, in both years. Total blooms were reduced in 1987, but not in 1988. Cotton maturity was delayed by triclopyr application during early bloom, as shown by a decrease in percent open bolls, and a decrease in first pick cotton yields. Cotton yield was lower in plots receiving triclopyr, with the greatest yield reduction caused by a 60 g ha-1triclopyr application at early bloom.

Field studies were conducted from 1988 to 1990 on a Sharkey clay to evaluate residual weed control in rice with quinclorac applied PPI, PRE to dry soil, and PRE to moist soil. Quinclorac applied at 0.4 or 0.6 kg ai ha−1PPI or PRE to dry or moist soil controlled more than 80% of barnyardgrass, pitted morningglory, and hemp sesbania without rice injury. Quinclorac applied at 0.3 kg ha−1controlled these three weed species substantially but inconsistently. No rice injury was observed from any quinclorac treatment. Except for one of three years when irrigation was delayed for 7 d after PRE application to dry soil, application timing did not consistently affect weed control or rice yield.

Two series of experiments were conducted from 1976 through 1978 on Marvyn loamy sand in central Alabama to determine the competitive relationship of yellow nutsedge (Cyperus esculentusL.) with cotton (Gossypium hirustumL. ‘Stoneville 213’). In the first series of experiments yellow nutsedge was left undisturbed or removed from plots to give periods of competition of 0, 2, 4, 6, 8, 10, and 25 weeks. Seed cotton yield was reduced 2 of 3 yr with full season (25 week) competition, but was unaffected by shorter periods of competition in all years. Main stem diameter of cotton was also reduced 2 of 3 yr when competing full season while main stem height was reduced in only 1 of 3 yr with full season competition. In the second series of experiments yellow nutsedge densities were monitored in 48 individual plots and regression analysis showed yields of seed cotton were consistently reduced with full-season competition. Yellow nutsedge shoot densities ranged from zero to 93 shoots/m2(measured 13 cm on either side of the drill) and approximately 18 kg/ha of seed cotton were lost for each additional yellow nutsedge plant per m2.

Cotton (Gossypium hirsutum) response was evaluated when quinclorac was applied prior to cotton emergence (preemergence) and to cotton in the cotyledon and pin-head square stages in 1988, 1989, and 1990. Quinclorac applications at 9, 17, 35, 70, and 140 g ha−1prior to cotton emergence had little effect on cotton growth, with only 140 g ha−1causing stand reduction or stunting. Quinclorac application to cotton in the cotyledon stage caused more damage, and 70 g ha−1caused crop injury. Greatest phytotoxicity was observed when quinclorac was applied to cotton at pin-head square, with all rates including 9 g ha−1causing injury. Cotton injury consisted of leaf strapping and malformation of reproductive structures. Regression analysis revealed yield was reduced by quinclorac applications to cotton in the cotyledon or pin-head square stage. The approximate regression equation to predict cotton yields after pin-head square application of quinclorac was [yield] = [yield with no injury] − 10(quinclorac rate in g ha−1).

Cotton (Gossypium hirsutumL.) was grown in the presence of common cocklebur (Xanthium strumariumL. # XANST) on a Lucedale fine sandy loam. Cotton was maintained weed free or allowed to compete with common cocklebur for 0, 3, 5, 7, 9, or 11 weeks after planting. Mathematical predictions of seed cotton yield were optimum when maintained free from common cocklebur interference for 8 weeks or more after cotton emergence in 1981 and 1982, and 10 weeks or more in 1980. Common cocklebur adversely affected yield when allowed to compete longer than 4 weeks in 1981 and 1982, and 2 weeks in 1980.