Response of non–bromoxynil-resistant cotton to reduced rates of bromoxynil

Field research was conducted for 2 yr to determine the effects of reduced rates of bromoxynil on growth and yield of non–bromoxynil-resistant cotton. Rates of 4.5, 9, 17, 35, 70, and 140 g ha−1, representing 0.008, 0.016, 0.031, 0.063, 0.125, and 0.25 fractions of the maximum labeled use rate per application (560 g ha−1), were applied to cotton at the two-, five-, or nine-node growth stage. Visual injury was reduced because application timing was delayed from two- to five-node stage in all experiments and from five- to nine-node stage in two of three experiments. Although negatively affected at all application timings, plant height reduction response decreased with increasing cotton maturity. Plant dry weight was most negatively affected after application at the two-node stage. Bromoxynil application, based on the node above white flower number, did not result in maturity delays but did promote earlier maturity when applied at 140 g ha−1 to two- and five-node stage cotton in one of the three experiments. Final plant population was reduced only at the two- and five-node timings, with response more pronounced at the initial timing. Seedcotton yield after bromoxynil application at the highest rate to two-leaf cotton was reduced 34% compared with other rates and the nontreated control. Bromoxynil applied to five- or nine-node cotton did not significantly reduce yield. Nomenclature: Bromoxynil; cotton, Gossypium hirsutum L. ‘Stoneville 474’, ‘DP 33B’.