دوره بحراني كنترل علف هاي هرز در مزرعه آفتابگردان (Helianthus anuus L)

Critical period of weeds control in sunflower, Helianthus annus L

In order to determine the critical period of weeds control in Allstar cultivar of sunflower, an experiment was conducted in experimental farm of Islamic Azad University of Tabriz, Iran, in 2007. The experimental design was a randomized complete block with three replications. The treatments were weed - infested and weed - free at 0, 2, 4, 6, 8, 10 and 14 weeks after sunflower emergence. Studied traits were hull weight to brain weight ratio, 100 grains weight, grain yield, oil percentage and oil yield. Results indicated the significant differences among treatments in most studied traits. Full season weed - infested treatment decreased up to 27.5% and 43% grain and oil yield in comparison to full season weed-free treatment, respectively. Based on fitted equations for weed-infested and weed - free plots, 1 to 9.5 weeks and 2.5 to 7.5 weeks after sunflower emergence were determined as critical periods of weed control with 5% and 10% yield loss, respectively.