The distance-of-influence of an individual devil's-claw plant to cotton leaf, stem, boll (reproductive parts), and combined aboveground plant parts was determined in two field experiments. The distance-of-influence could not be detected for the first 6 weeks after emergence; by 9 to 12 weeks, it extended up to 25 cm or more; and by the end of the season, up to 50 cm on each side of the weed. Cotton leaf and stem weights were less sensitive than cotton boll weights for measuring distance-of-influence from devil's-claw. At maturity, cotton boll weight was reduced 62 and 51% in 1983 and 45 and 29% in 1984 for sampling intervals of 0 to 25 and 25 to 50 cm, respectively. Interference from cotton reduced devil's-claw stem weight, seed capsule weight, and whole plant biomass by 6 weeks after emergence and reduced leaf biomass by 9 weeks in 1983. All except stem biomass were affected in 1984. Distance-of-influence and weed-density interference studies predicted lint yield loss similarly.
