Studies were conducted at Clayton, Lewiston, and Rocky Mount, NC, to evaluate weed and cotton response to herbicide systems in bromoxynil-resistant Stoneville BXN 47 cotton. Herbicide systems that included clomazone preemergence (PRE) controlled broadleaf signalgrass, common lambsquarters, common ragweed, goosegrass, large crabgrass, and prickly sida greater than 88%. Inconsistent Palmer amaranth control was observed with the addition of fomesafen PRE to clomazone PRE and pendimethalin preplant-incorporated (PPI) herbicide systems. Addition of bromoxynil early postemergence (EPOST) to clomazone and pendimethalin systems increased ivyleaf morningglory control to greater than 84% and provided higher yields than did the same systems without bromoxynil. Bromoxynil EPOST followed by (fb) cyanazine + MSMA late postemergence directed (LAYBY) improved weed control in clomazone and pendimethalin systems. Clomazone PRE and pendimethalin PPI with or without fomesafen PRE fb bromoxynil EPOST fb LAYBY herbicides controlled weeds and yielded equivalent to the standard herbicide system of pendimethalin PPI fb fluometuron PRE fb bromoxynil EPOST fb LAYBY.

The effect of CGA-362622 on annual grass control in cotton by clethodim and fluazifop-P and crop response was determined in field studies. CGA-362622 applied postemergence at 5.3 g ai/ha injured cotton up to 34% 1 wk after treatment (WAT). Injury was similar when crop oil concentrate (COC) and nonionic surfactant (NIS) were included. Adding fluazifop-P, but not clethodim, to CGA-362622 increased crop injury. Cotton recovered by 3 WAT. CGA-362622 mixed with fluazifop-P at 210 g ai/ha reduced broadleaf signalgrass and large crabgrass control 60 to 80%. Control was similar with COC or NIS in the mixture. Increasing the fluazifop-P rate to 315 g/ha did not improve control. CGA-362622 mixed with clethodim at 105 g ai/ha reduced control 65 to 80% with NIS and 40 to 65% with COC. Increasing the clethodim rate to 175 g/ha, especially with COC, substantially increased control. However, control was still less than that with clethodim at 105 g/ha. Prometryn plus MSMA postemergence-directed 3 wk after gramincide and CGA-362622 application increased control. Cotton yield was similar with clethodim alone and clethodim at 175 g/ha plus CGA-362622. Yield was reduced 29% by CGA-362622 mixed with fluazifop-P at 350 g/ha. Control was reduced by CGA-362622 applied 1 d before or after clethodim but not 5 d before or after clethodim. Control by fluazifop-P was reduced by CGA-362622 applied 1 or 5 d before or 1 d after the graminicide. Under greenhouse conditions, CGA-362622 and pyrithiobac mixed with clethodim, fluazifop-P, quizalofop-P, or sethoxydim reduced control of large crabgrass. Greater antagonism was noted with CGA-362622 than with pyrithiobac, and with fluazifop-P and quizalofop-P than with clethodim or sethoxydim.

Studies were conducted to determine the effect of interference between Pennsylvania smartweed and cotton on plant growth and productivity. Pennsylvania smartweed remained shorter than cotton until at least 80 d after cotton planting. However, Pennsylvania smartweed produced considerable dry biomass by cotton harvest. Pennsylvania smartweed biomass per plant was not affected by weed density when grown with cotton. When grown alone, Pennsylvania smartweed produced 1,640 and 2,060 g dry biomass plant−1 depending on the year. This biomass was over four times greater than the biomass produced by plants grown with cotton. Cotton lint yield decreased between 1.3 and 1.1 kg ha−1 with each gram increase in weed dry biomass per meter of row. The relationship between Pennsylvania smartweed density and cotton percent yield loss was described by the hyperbolic function. The estimated coefficients a (maximum yield loss as density approaches infinity) and i (yield loss per unit density as density approaches zero) were 102 ± 23 and 51 ± 12, respectively, in 1998 and 53 ± 1 and 98 ± 5, respectively, in 2000. Pennsylvania smartweed achene production was also described by the hyperbolic function. Estimated achene production at 1 plant m−1 cotton row was 18,000 and 26,000 achenes m−2 in 1998 and 2000, respectively.

Field studies were conducted at two North Carolina locations to determine the effect of interference between pale smartweed and cotton on plant growth and productivity. Pale smartweed remained shorter than cotton until at least 70 d after cotton planting. However, pale smartweed grew over twice as tall as cotton and produced considerable dry biomass by cotton harvest. Pale smartweed biomass per plant was not affected by weed density up to 3.5 plants m−1 of row when grown with cotton. Cotton competition reduced pale smartweed dry biomass per plant at least 400%. The relationship between pale smartweed and cotton percent yield loss was described by the rectangular hyperbola model with the asymptote (coefficient a) constrained to 100% maximum yield loss. The estimated coefficient i (yield loss per unit density as density approaches zero) was 29 ± 4 and 23 ± 4 in 1998 and 2000, respectively. Pale smartweed achene production was also described by the hyperbolic function. Estimated achene production of smartweed at 1 plant m−1 cotton row was 63,000 and 25,000 achenes m−2 in 1998 and 2000, respectively.