Euphorbia heterophylla (wild poinsettia), and, more recently, Ipomoea ramosissima (morningglory) are among the main weeds infesting soybean crop in southern Brazil. This work aimed to evaluate the effects of wild poinsettia and morningglory as single or mixed populations in coexistence with soybean. Two experimentswere conducted to compare associations of wild poinsettia or moningglory with soybean, using five ratios of wild poinsettia plants and soybean or morningglory (0:8, 2:6, 4:4, 6:2 and 8:0). In a third experiment, four soybean plants per pot were kept constant and five ratios of of wild poinsettia and moningglory plants were used (0:8, 2:6, 4:4, 6:2 and 8:0), established in two weed emergence periods related to the soybean. The results indicated that a higher reduction in soybean biomass was caused by morningglory than by wild poinsettia, when these species were established before the crop. In mixed communities, morningglory is more competitive than wild poinsettia.
weeds; competitive ability; wild poinsettia; morningglory
