اثرتاریخ کاشت و دوره بحرانی مهار علف های هرز بر رشد و عملکرد آفتابگردان

In order to investigate the effect of planting (sowing) date and critical period of weed control on sunflower growth and yield, an experiment was carried out in 2012 growing season at Shiraz University. The experimental design was split plot based on randomized complete block with four replications. Main plot was planting date in three levels (June 16th, 23th and 30th) and sub plot was in 6 levels (weedy & weed free, until 6 and 9 leaves stage and during the growing season). Effect of planting date and critical period on biological yield, showed that increase of competition period of weeds with this crop, decreasing was significantly. Max and min grain weight 49.91 and 38.62 mg, respectively, were observed on first and second planting date. Over planting dates, oil function in (23, 30 June) respectively 14.1 and 19.68 percent and by increase the period of crop weed competition, there was a significant reduction in oil function. Grain yield was also significantly reduced with delay in planting date. Final result showed that the first planting date was the best date and with passage of time and increase weed competition, significant decreases were observed for most traits.