EFFECT OF FOLIAR APPLICATION OF Zn AND B ON FRUIT PRODUCTION AND PHYSIOLOGICAL DISORDERS IN SWEET ORANGE CV. BLOOD ORANGE

To study the effect of Zn and B as foliar spray on growth and yield of sweet orange, cv. Blood red at Dargai, Malakand Agency, Pakistan during 2006 and 2007. The micronutrients zinc (Zn) in the form of zinc sulphate (ZnSo4.7H2O) as zinc source at the rate of 0.5 % and 1.0 % and boron (B) in the form of boric acid (H3BO3) at the rate of 0.02 % and 0.04 % were applied as foliar spray at three different stages of plant growth i.e before flower initiation, after fruit set when it becomes berry size and at 40 days interval of second spray. The solution was prepared containing 0.8 % urea and 0.1 % surf as wetting agent. The experiment was laid out in randomized complete block design. The foliar application of Zn and B significantly influenced the days to flowering, fruit yield tree^-1, % dieback, % chlorosis, and % rosette plant^-1, whereas days to fruit set, % fruit set and % fruit drop were not significantly affected by foliar spray of Zn and B alone or either in combination. The maximum fruit yield plant^-1 was obtained when high concentration of zinc (1.0 %Zn) with low concentration of boron (0.02 %B) applied to the plants. The maximum days to flowering were obtained in plants treated with foliar Zn, whereas, the combination of Zn and B as foliar spray significantly reduced the % dieback, % chlorosis and % rosette tree^-1. The low conc. of Zn (0.5%) in combination with high conc. of B (0.04%) positively reduced the % dieback, % chlorosis and % rosette tree^-1. A significant variation was observed in control of physiological disorder during two years. Therefore, it is concluded that the foliar application of zinc in combination with boron may be applied in order to increase the production and to control the decline of citrus orchard in Dargai region particularly and in Pakistan generally to maximize the yield and extend the bearing life of citrus plants.