Abstract
SummaryFoliar-spraying apple trees with zinc sulphate in autumn, or dormant-season spraying in February, did not increase leaf Zn in the ensuing growth. Foliar application during the growing season increased the Zn content of the sprayed leaves even if they were just beginning to grow at the time of spraying. Spraying Zn–EDTA when the apical bud was bursting did not increase Zn in leaves produced from the lateral buds. Placement of zinc sulphate in holes 30–60 cm from the trunk at the time the apical bud was bursting significantly increased leaf Zn in the early spring growth. However, such increase was only observed if the trees were irrigated soon after application. It is suggested that following such application Zn enters the tree by mass flow through the cut roots. In certain cases raising the Zn level to a concentration of 130–160 ppm Zn in the leaves was associated with toxicity, the symptoms of which are described.
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