GROWTH AND INTERACTION OF BARNYARDGRASS (ECHINOCHLOA-CRUS-GALLI) WITH COTTON (GOSSYPIUM-HIRSUTUM)

Several weed-free and barnyardgrass competition periods were established and maintained in cotton in field plots to evaluate their influence on cotton yield and seed production of barnyardgrass. When barnyardgrass was sprayed with fluazifop 3, 6, 9, or 12 weeks after cotton emergence, only plots sprayed at 3 weeks yielded as much cotton as plots kept weed free. Barnyardgrass permitted to compete for 6, 9, 12, and 25 weeks reduced cotton yields an average of 21, 59, 90, and 97%, respectively. When barnyardgrass was seeded into weed-free plots at 3, 6, 9, and 12 weeks after cotton emergence, a weed-free period of 9 weeks was required to prevent significant cotton yield reduction. Cotton in plots weed free for 3 and 6 weeks yielded an average of 13 and 87% as much seed cotton, respectively, as weed-free controls. Barnyardgrass produced 15 to 85% as many seeds as weedy check plots in plots weed free for less than 9 weeks and in plots where control was delayed for 9 and 12 weeks. Cotton grades were reduced because of grass in plots weed free for 3 and 6 weeks, and in plots where barnyardgrass competed for 9 and 12 weeks.