The Effect of Calcium Chloride, Prohexadione-Ca, and Ca-coated Paper Bagging on Reduction of Bitter Pit in 'Gamhong' Apple

'Gamhong' is a midseason, high fresh eating quality red apple (Malus domestica Borkh.) that has high popularity in Korea. 'Gamhong' however is prone to bitter pit or russet. Over two growing seasons, different types of calcium (Ca) were applied in either soil or foliar spray to 5 year-old 'Gamhong'/M.26 apples which had severe bitter pit in 2004. We sprayed calcium chloride (CaCl2), prohexadione-Ca (Pro-Ca) to soil or leaves, and covered fruits with Ca-coated paper bags in 2005. Drenching lime stone liquid or CaCl2 solution on soil were not effective in the reduction of bitter pit, while foliar spraying two times of 0.5% CaCl2 before paper bagging was effective in the reduction of bitter pit while increasing Ca content of peels. Great effect on reduction of bitter pit and on enhancement of Ca content in peels was attained by three different treatments: leaves spraying of 0.5% CaCl2 three times before bagging; Pro-Ca spraying five days after full blooming; and Ca-coated paper bagging 4-5 weeks after full blooming. However, the best result was shown by foliar spraying three times of 0.5% CaCl2 followed by Ca-coated paper bagging.