What is bitter pit?
Bitter pit affects apple trees. The apples have dark spots on the skin or in the flesh, or both. The brown areas of the flesh have a bitter taste. It affects certain varieties, and it can increase greatly during storage. Varieties that are particularly susceptible include Bramley’s Seedling, Cox’s Orange Pippin, Egremont Russet, Merton Worcestor and Newton Wonder. The varieties Jonagold and Gala seem to be unaffected by bitter pit.
How to prevent bitter pit
Bitter pit is a disorder caused by low calcium levels. If you have a problem with bitter pit, you can spray the tree with a calcium salt such as calcium chloride or calcium nitrate from mid-June to mid-September. But the disorder can also be prevented by good tree management. When apples are growing on the tree, every morning, water leaves the apples and moves to the leaves, returning in the late afternoon. The more leaves per apple on the tree, the more water (and calcium) leaves the apple, and the higher the likelihood of some of that calcium not being returned. So bitter pit can be caused by a light crop, which can in turn be due to poor pollination. It can also be caused by dry soil conditions, and incorrect use of fertilizer. Summer pruning is a good way of reducing the vigour of the canopy. Apply a mulch around the tree to retain moisture. Water or irrigate the tree as necessary. Use a balanced fertilizer. Pick the fruit when it is fully ripe.