Recommended prebioom copper spray has no beneficial effect on ‘delicious’ apple tree copper status or fruit typiness

Abstract

Three field experiments were conducted to evaluate a new commercial recommendation to add small amounts of a Cu(OH)₂‐based fungicide, Kocide 101, to prebioom zinc (Zn) nutrient sprays in order to enhance ‘Delicious’ apple tree copper (Cu) status and improve fruit typiness. Treatments were (1) single prebioom spray of basic Zn sulfate in combination with varying rates of added Cu as Kocide; (2) single spray of Kocide alone at pink timing; and (3) single silver‐tip spray of Zn sulfate in combination with varying rates of Kocide or a more soluble Cu sulfate‐based product. The Cu sprays applied at silver‐tip had little or no effect on flower cluster Cu concentration at full bloom. Kocide applied at green‐tip and later increased flower cluster Cu. None of the Cu sprays influenced midsummer leaf Cu concentration. The Cu sprays had no beneficial effect on fruit mass or on any of five fruit typiness indices. The experimental results indicate that there are no detectable nutritional or fruit typiness benefits resulting from adding Kocide to Zn sprays at any prebioom timing, or from adding Cu sulfate to Zn sprays applied at silver‐tip bud stage.