Competitive effects of redroot pigweed (Amaranthus retroflexus) on three sunflowers (Helianthus annus) cultivars

In order to study the effects of redroot pigweed on three cultivars of sunflower, an additive experiment were conducted in 2008. This experiment was done in split plot based on randomized complete block design with three replications. Treatments were weed densities in main plots (0, 2, 4, 8 and 16 plants per row) and sunflower varieties in sub plots (Record, Armavirovski and Zaria). Hyperbolic model was used to assess the effect of redroot pigweed on sunflower yield. Results of this investigation showed that traits were affected by 8 and 16 redroot pogweed plants per row, significantly. Among the varieties, Zaria had the highest seed yield, oil percentage, total dry matter and 1000 seed weights. In general, Zaria was could tolerate various densities of redroot pigweed better than Record and Armaviroski varieties.