Calcium deficiency has never been identified in California peach orchards. Most soils in the San Joaquin Valley are abundantly supplied with Ca and leaf samples generally show levels well above the deficiency threshold (1.0%). Deficiency symptoms from seedling hydroponics experiments have been described as large necrotic areas on the leaves. We were never able to induce Ca deficiency in our sand tank experiments.
In field trials with multiple sprays of calcium formulations (Foliar Calcium Sprays), we were able to increase Ca levels in leaves and fruit skins, but this had no effect on fruit quality, disease resistance or storage life. In other experiments, certain rootstocks were able to significantly increase Ca fruit levels, but again this had no effect on any measure of fruit quality (Ferrari Master's Thesis on Calcium and Disease).