Effect of tumble pigweed (Amaranthus albus L.) competition on yield and yield components of sunflower (Helianthus annuus L.) cultivars in Birjand

In order to evaluate the effect of tumble pigweed competition on yield, yield components and seed quality of six cultivars of sunflower; an experiment was conducted with factorial layout based on a completely randomized block design at the research farm of College of Agriculture, University of Birjand in 2012. The factors were four weed densities (0, 5, 10 and 15 plants/m2) and six cultivars of sunflower (Azargol, Jame Isfahan, Syrna, Farrukh, Progress and Euroflour). The results showed that by increasing weed density, yield and yield components of sunflower were decreased. By increasing weed density from zero to 15 p.m2, grain yield of sunflower was decreased up to 40.2%. Jame Isfahan cultivar produced the highest seed yield (5.789 kg/ha), and Farrukh cultivar had the least percentage of seed yield loss in weed density of 15 p/m2. Generally, Progress, Euroflour and Jame Isfahan cultivars had the most competitiveness and Azargol cultivar showed the least competitiveness against tumble pigweed.