Productivity, growth, and leaf mineral composition of orange and grapefruit trees foliar‐sprayed with zinc and manganese

Benefits of ZnSO4 and MnSO4 foliar sprays were studied for four years in one ‘Valencia’ orange (Citrus sinensis Osbeck) and two ‘Ruby Red’ grapefruit (Citrus paradisi Macf.) orchards in the lower Rio Grande Valley of Texas, applying annually from one to three sprays at concentrations equivalent to 216 and 168 ppm metallic Zn and Mn, respectively. Leaf Zn in control ‘Valencia’ trees in Experiment 1 varied from 13–26 ppm d.w. and Zn deficiency patterns were affecting 1–2 % of the canopy. Leaf Zn level in control grapefruit trees varied between 17–46 and 12–31 ppm d.w. in Experiment 2 and 3, respectively. Trees in Experiment 2 showed no Zn deficiency symptoms and in Experiment 3 the symptoms were transient and obscured by patterns of B excess. Zn foliar sprays were effective in correcting Zn deficiency symptoms and in elevating leaf Zn content to an optimum range. However, both the orange and grapefruit trees failed to respond to Zn sprays in terms of yield, fruit number, average fruit weight, and canopy height and width. In all experiments leaf Mn of the control trees ranged from 25 to 39 ppm and in neither experiment were Mn deficiency patterns observed. Mn sprays produced no benefits even though they increased leaf Mn level. In some years, Zn and Mn were translocated from sprayed to new leaves to increase their concentration by 2–5 ppm.