FULL-SEASON PALMER AMARANTH (AMARANTHUS PALMERI) INTERFERENCE WITH COTTON (GOSSYPIUM HLRSUTUM)

Laval M. Verhalen Department of Plant and Soil Sciences, Oklahoma State University, Stillwater, OK 74078 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-l 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 Altus 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-' (or 10.7%) and 58 kg ha-1 (or 11.5%) at Perkins and at Chickasha in 1996, respectively. At Perkins and Altus in 1997, for each 1 weed row-1, lint yield was reduced 71 kg ha-1 (or 5.9%) and 112 kg ha-' (or 8.7%), respectively. Lint yield vs. end-of-season weed volume fit a linear model except at Altus in 1997. For each increase of 1 m3 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 (s 6 weeds), each increase of 1 m3 of weed plot-' reduced lint yield 1.6 and 2.3%, respectively. Lint yield vs. end-ofseason 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-'. 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.