COMPETITIVE ABILITY AND THRESHOLD LEVELS OF 3 BROADLEAF WEED SPECIES IN SUNFLOWER

Data collected from field trials carried out in different years and environments were used to determine competitive ability and threshold levels of Ammi majus L., Chenopodium album L. and Sinapis arvensis L. The hyperbolic model showed a good fit to the experimental data. The three broadleaf weeds showed low and similar competitive indices (i ranging from 1.08 to 1.75), supporting the hypothesis of a high sunflower competitive ability. The economic threshold was four to six plants m(-2) for all three weeds in the case of weed control by hoeing and about six plants m(-2) for S. arvensis in the case of a postemergence treatment with imazamethabenz. Limitations and approximations in estimating competitive parameters are pointed out and discussed.