Cork Spot and Bitter Pit Fruit Disorders

Cork spot and bitter pit in York Imperial, Delicious, and Golden Delicious apples, along with other calcium-deficiency physiological disorders, continue to cause apple producers economic losses. These disorders appear to be specifically related to low levels of calcium and sometimes high levels of nitrogen in the fruit flesh. Fruit flesh calcium content is influenced by many factors. Good horticultural management techniques that improve soil conditions, encourage uniform annual cropping, and encourage moderate tree vigor will decrease calcium-related fruit disorders.

Corking, characterized by spherical dead areas in the flesh, is an orchard disorder, while bitter pit is primarily a storage disorder and usually attacks the skin and adjacent cells. However, symptoms vary according to area, variety, and environmental conditions, making this distinction less than clearcut.

While corking is worse under conditions of low calcium, lack of calcium does not appear to be the sole cause. Corking is worse under conditions of excessive tree vigor or moisture stress and has been most severe on Delicious and York Imperial. Bitter pit is worse on Golden Delicious and is aggravated by early harvest.

During the past 20 years much research has been conducted on calcium nutrition of apples in South Africa, Australia, New Zealand, England, and the United States. From this research, as well as research conducted in Pennsylvania, a comprehensive program is recommended to reduce corking and bitter pit.

A program to control bitter pit and corking should involve almost all cultural practices conducted in apple production, since no one practice guarantees control of the disorder below the economic injury level. An effective program should be based on the consideration of all five factors explained below since in any specific orchard block one factor could be primarily responsible for the problem. Growers are urged to use these recommendations when the cost of control practices is less than losses from the disorders.

The five points in the program are listed as a person should think of them in the life of an orchard and not in order of effectiveness. Calcium chloride sprays, though listed last, offer many advantages over other parts of the program mainly because they can be started in June the year of harvest, while some of the other practices take years to accomplish.



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