This corky area will usually extend into the flesh. Cork spot can also be internal in Yorks. The problem is associated with early-season water stress, irregular cropping, excessive tree vigor and poor nutrition. The disorder is initiated by midseason and does not develop after harvest. Bitter pit is characterized by numerous small sunken pits of collapsed tissue softer than the apple flesh.
Most pits are just beneath the skin, mostly on the blossom end of the fruit.
The problem is associated with late-season moisture stress conditions, and fruit harvested too early is more prone. Bitter pit does not usually develop until after harvest. At 15-19 pounds per acre per year, some cork spot and bitter pit control will be achieved, but storage life will not be enhanced. The standard rate to apply in blocks where these disorders are chronic is 20-29 pounds per acre per year. The 30-39 pound rates will give fairly good control of corking and bitter pitting most years.