Redroot Pigweed (Amaranthus retroflexus L.) Interference with Sunflower Hybrid, Allstar RM

In order to study the influence of redroot pigweed interference with sunflower, Allstar RM hybrid, an experiment was carried out at research station of Islamic Azad University of Tabriz in 2004, with three different densities of 5, 15 and 25 plants per meter of row and three interference times of emerging with sunflower, 15 and 30 days after sunflower emergence in a distance of 15 cm from both side of the sunflower rows. The experiment was established as a factorial based on randomized complete block design. Analysis of variance indicated that stem height at the ripening stage, antodium diameter, seed number in each antodium, hollow seed percentage, 1000 kernels weight, grain yield, seed oil percentage and oil yield were affected by density and interference time of redroot pigweed. Interaction of density×interference time on stem height at the ripening stage, 1000 seeds weight, grain yield, seed oil percentage and oil yield were significant. The lowest and highest hollow seed percentage obtained from density of 5 plants per meter of row at 30 days after sunflower emergence and full season interference of 25 plants per meter of row, respectively. The highest seed number in each antodium was obtained in the second level of density. The highest 1000 seeds weight and grain yield observed from density of 5 plants m-1 of row and interference time of 30 days after sunflower emergence. Seed oil percentage in all treatments except density of 5 plants per meter of row and interference time of 30 days after sunflower emergence had significant difference in comparison with the control. It seems that, weed plant number has higher effect than weed interference time on seed oil percentage. This research showed that in studied cultivar, with the short height, lower leaf area and lower competition ability with redroot pigweed, yield loss is affected more by density than interference time.