Low-residue micronutrient sprays for citrus

Applications of zinc, manganese, and copper compounds to alkaline California soils have not proven consistently effective in supplying these elements to citrus trees. However, commercially formulated compounds and mixtures containing zinc, manganese and copper in proper concentrations readily supply adequate amounts of these nutrients when used in foliar applications. Such sprays, in which precipitating agents are combined with ZnSO₄, MnSO₄ and CuSO₄, are relatively high in salts, but low in metallic ions in solution, as shown in tests reported here. Such sprays leave large amounts of residue on the leaves, and because of this undesirable effect, these studies were undertaken to develop safe, low-residue micronutrient sprays.