Boron Deficiency in Apple
Boron deficiency commonly causes cracking and external cork symptoms on the fruit even though there may be no symptoms on the foliage, such as rosetting of thickened brittle leaves and dieback of the growing points. Premature fruit drop occurs and fruit quality can be badly impaired by the cork formation. When the internal cork develops early in the season, the affected fruit will become badly deformed.
In severe cases, dead areas appear in the bark of young branches (apple measles). The bark may be rough and cracked. Boron deficiency may affect the translocation of calcium in the tree, and in this way boron deficiency may be associated with “bitter pit."