Dr. Guy Witney- Former WSU Area Extension Faculty
Severe drought during late fruit cell division and rapid cell enlargement in apple trees can cause irreversible damage to developing fruit. The cells furthest from the fruits’ water conducting elements (vascular bundles) become deprived of water and die. The resulting symptoms include bitter pit-like spots and severe tissue deformation near the calyx end of the fruit (see photo below). Most often just one or two trees are found with these symptoms on fruit resulting from a sprinkler blockage or other temporary interruption of irrigation water. In the worst cases whole sections of a block may be damaged because of a broken lateral line or error in irrigation scheduling.
Unfortunately, it may take three to six weeks for the symptoms to be noticed at which time it is far to late to take any corrective action. Because of this time delay, an error in irrigation management may be difficult to identify.