Managing Bitter Pit in 'Honeycrisp' Apples Grown in the Mid-Atlantic United States with Foliar-applied Calcium Chloride and Some Alternatives

Three separate experiments were conducted to test standard calcium chloride salt (CaCl2) rates and several new formulations of calcium (Ca) for amelioration of bitter pit, a Ca-related physiological disorder that affects fruit of many apple (Malus xdomestica) cultivars, including the popular cultivar Honeycrisp. Even small amounts of bitter pit damage make apples unmarketable. We evaluated various formulations of Ca to compare their effectiveness in controlling bitter pit, including proprietary Ca products (InCa (TM), Sysstem-Cal (TM), Vigor-Cal (TM), XD10, and XD505) with and without antitranspirant. Calcium chloride is the most common Ca product used to reduce bitter pit incidence, but it has negative impacts, such as phytotoxicity and corrosiveness. Of the products that were tested in 2011, XD10 at the high rate and XD505 are candidates for future study. In 2012, both the CaCl2 and XD10 treatments had lower bitter pit severity than the nontreated control, but only the CaCl2 treatments had a lower total percentage of fruit with bitter pit compared with the control. The antitranspirant reduced bitter pit incidence in one of three treatments. Full season Ca treatments and higher rates (up to 23.5 lb/acre per season of elemental Ca) are needed to significantly reduce bitter pit incidence in 'Honeycrisp' apples in the mid-Atlantic United States.