AbstractThe competitiveness of hemp sesbania (Sesbania exaltataRaf. RYBD. EX A. W. Hill) with sunflower (Helianthus annuusL.) grown in two row spacings was evaluated at the University of Arkansas at Pine Bluff Agricultural Experiment Station in 1982 and 1983. Sunflower and hemp sesbania at densities of 3 to 5 and 13 to 16 plants per meter row, respectively, were interseeded in 61 and 91 cm row spacings in field test plots. Hemp sesbania plants were removed at different sunflower growth stages. In 1982, weed removal treatments were: (1) weedy check, (2) weed‐free check, (3) weed removal at 15‐leaf stage, (4) removal at 20, (5) 50 and (6) 100 sunflower anthesis. Treatments in 1983 consisted of: (1) weedy check, (2) weed‐free check, (3) weed removal at 10‐leaf stage, (4) bud stage, (5) pre‐anthesis, (6) 10 anthesis, and (7) 100 anthesis. Sunflower yields were significantly decreased by hemp sesbania competition each year, except for the weed competition treatments in 91 cm row spacing in 1982. Generally, the longer the weeds were allowed to compete with sunflower, the greater the sunflower yield reduction. Yield reductions of 5 to 6 and 25 or more were observed when hemp sesbania was allowed to compete with sunflower until the 10‐leaf and anthesis stages of sunflower growth, respectively. When hemp sesbania was allowed to compete with sunflower for the entire growing season, yield was reduced by as much as 35. Reducing row width from 91 cm to 61 cm did not improve sunflower's ability to compete with hemp sesbania. Thus, hemp sesbania is quite competitive with sunflower and should be controlled during early vegetative growth in order to minimize
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