The effect of tree sprays of calcium, boron, zinc and naphthaleneacetic acid, alone and in all combinations, on the incidence of storage disorders in Merton apples

Abstract

The effect of four whole-tree sprays at monthly intervals on the fruit mineral element content and on the incidence of storage disorders in Merton apples was investigated for three years. Calcium nitrate, boric acid, zinc nitrate and naphthaleneacetic acid (NAA) were applied singly and in all possible combinations. There were no significant treatment interactions, which implied an absence of synergistic or antagonistic effects between spray components. Calcium nitrate was the only compound whose application consistently reduced the incidence of bitter pit and breakdown following cool storage for 4 months. In one year NAA reduced the incidence of these disorders, but it also reduced mean fruit size and increased the concentration of most of the mineral elements, including calcium, in the fruit at harvest. Zinc nitrate sprays had no effect. Boron application promoted the development of core flush in one year and of breakdown in two years, but did not affect the incidence of bitter pit. No relationship was observed between the levels of calcium and boron in the fruit.