Full-season Palmer amaranth (Amaranthus palmeri) interference with cotton (Gossypium hirsutum)

Four field experiments were conducted in Oklahoma to measure full-season Palmer amaranth interference on cotton lint yield and fiber properties. Density of the weed ranged from 0 to 12 plants 10 m −1 of row. Cotton lint yield vs. weed density fit a linear model for densities ⩽ 8 weeds row −1 at Perkins and Chickasha in 1996 and at Alms in 1997. At Perkins in 1997, all densities fit a linear model. For each increase of 1 weed row −1 , lint yield reductions were 62 kg ha −1 (or 10.7%) and 58 kg ha −1 (or 11.5%) at Perkins and at Chickasha in 1996, respectively. At Perkins and Alms in 1997, for each 1 weed row −1 , lint yield was reduced 71 kg ha −1 (or 5.9%) and 112 kg ha −1 (or 8.7%), respectively. Lint yield vs. end-of-season weed volume fit a linear model except at Alms in 1997. For each increase of 1 m 3 of weed plot −1 , cotton lint yield in 1996 was reduced by 1.6 and 1.5% at Perkins and Chickasha, respectively. In 1997 at Perkins and Altus (⩽ 6 weeds), each increase of 1 m 3 of weed plot −1 reduced lint yield 1.6 and 2.3%, respectively. Lint yield vs. end-of-season weed biomass fit a linear model in all four experiments. Lint yield was reduced 5.2 to 9.3% for each increase of 1 kg of weed biomass plot −1 . Fiber analyses revealed significant differences for micronaire (fiber fineness) among weed densities in two experiments, marginal significance in a third, and none in a fourth. An intermediate number of weeds often resulted in improved fiber micronaires in these environments. No other fiber properties were influenced by weed density.