Determination of the critical period for weed control in sunflower (Helianthus annuus cv. Record)

A field experiment was conducted to determaine the critical period for weed control in sunflower in Borugerd in southwestern Iran in 1999 cropping season. Treatments included weed free and weed interferance periods up to 10, 20, 30, 40 days after emergence and weed free during growing season. Treatmensts were replicated four times in a complete randomized block design. Gampertz and Logestic equations were fitted to weed free and weed interference data. Results showed a critical period of weed control based on 5% and 10% of acceptable yield loss from 10-43 and 18-33 days after emergence (DAE) equal to 250-1250 and 300-950 GDD or V2 to R1 and V2 to V9 stages, respectively. Weed inteference reduced the height, oil and kernel yield. Oil percent was not affected by weed interference or control.