Competitiveness of noogoora burr and fierce thornapple in irrigated cotton was assessed using area-of-influence methodology. Lint yields were regressed against distances from the weeds using spline regression. The resulting regression curves were used to estimate areas of influence and yield losses, which were further modeled as functions of weed size to understand weed competitiveness. Cotton lint yield reductions averaged 36 and 12%, with maximum distances of influence of 1.71 and 1.65 m for noogoora burr and fierce thornapple, respectively. Economic thresholds for control using hand hoeing were related to weed size. Thresholds for average-size weeds were one cocklebur in 195 m and one fierce thornapple in 73 m of cotton row.
