Trees low in Mg may have interveinal chlorosis on older leaves that appears in a herringbone pattern. The base of the leaf petiole may exhibit an inverted V-shaped green area. The randomly distributed irregular necrotic spots distinguish NLB in the early stages over the leaf surface. Heavy application of K can result in reduced Mg levels. 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.