The Delicious cultivar is quite susceptible to excess Mn. Symptoms occur on the bark as raised pimples. These enlarge and crack and lead to a rough, scaly bark. Because these elements are immobile, deficiency symptoms will first appear in the younger terminal leaves. Both nutrients are immobile, thus foliar symptoms appear first in the young terminal leaves.
Boron deficiency can lead to terminal dieback and a necrotic bark condition.
In addition to tree observations, take note of fruit quality during the growing season. Small fruit size may be a result of low N. Poor color on red cultivars can be an indication of low K levels. Cutting the fruit tissue reveals a corky tissue beneath. Bitter pit is generally confined to the calyx end of the fruit and occurs near the surface. Good observation is a valuable and necessary part of any nutrient-management program, but observation alone should not be relied upon to develop your program.