Bitter pit is a physiological disorder believed to be induced by calcium deficiency in apple fruits.
The incidence of bitter pit usually occurs during storage,[1] but in some cases it can also develop at harvest. This disorder has been studied for more than a hundred years and many approaches have been attempted to explain bitter pit development, but no one completely succeeded. The fact that total calcium in the fruit is not able to accurately predict bitter pit incidence has puzzled many scientists for a long time. The high correlation with no predictive accuracy between calcium and bitter pit make the development of this disorder one of the most complex and challenging mechanisms present in plants.
There are a few ways of preventing bitter pit from affecting apple and plant trees. The most effective way of prevention is spraying the trees (usually apple or pear) with calcium chloride or calcium nitrate. This method was developed by the Agricultural Research Service in Washington. This is so effective because Bitter Pit becomes a problem when trees undergo periods of stress, usually caused by severe weather, they sacrifice their current crop in order to survive. The trees extract calcium from the fruit and use it to survive. The result is calcium-depleted fruit, because the trees do not replenish the calcium lost in the fruit.