Effect of defoliation on the yield and yield components of sunflower

Experiments were conducted in the Peshawar Valley to study the effect of defoliation on the yield and yield components of sunflower and to simulate the damages caused by hail storm or insect pest. Sunflower hybrid, Peshawar-93 was planted in the NWFP Agriculture University while inbrid line TMS 11 was used at the Agriculture Research Institute, Tarnab during spring 1996. Experiments were laid out in RCB design with 4 replications. Days to maturity, plant height head diameter and yield (kg/ha) was significantly affected by various degree of defoliation, where as days to 50% flowering were not affected. Taller plant, large head diameter, maximum days to maturity and maximum yield (kg/ha) were recorded in plots receiving no defoliation. Non-significant differences in yield were observed between no defoliation and 50% defoliation without flag leaf which means that if 50% leaf area of sunflower plant is lost due to some hazard it will not bring a significant loss in yield of sunflower. At the same time significant differences in yield was observed between 50% defoliation and 100% defoliation without flag leaf. This indicates that in sunflower not only the flag leaf is important but other leaves also playa major role in photosynthetic activity.