Bitter pit can be caused by low soil moisture, low leaf calcium, or an imbalance between calcium and potassium within the leaves. Additional calcium can be soil or foliar applied. Soil application of gypsum is the most effective way to supply calcium on established orchards. Gypsum provides more available calcium within the root zone or subsoil than surface-applied lime. However, gypsum is not a liming agent and cannot be substituted for lime to raise the pH. Moreover, gypsum will not correct bitter pit caused by extended dry weather for the current crop.
Foliar application is the most effective way to increase calcium for the current growing season.
Use calcium chloride when tissue analyses show a high nitrogen content. Foliar treatments should be made at two-week intervals starting at first cover spray and ending two weeks prior to harvest. If leaf burn is observed, reduce the rate of calcium applied. For new orchards, phosphorus amendments should be incorporated deeply into the soil before trees are set. Deep incorporation enhances root growth and uptake efficiency.