Chlorosis

Chlorosis is a symptom of plant disease in which normally green tissue is pale, yellow, or bleached due to a lack of chlorophyll. 

Possible causes of chlorosis include poor drainage, high alkalinity, damaged or compacted roots, and nutrient deficiencies in the plant.

Some other results of chlorophyll underdevelopment are due to a lack of an essential mineral or oxygen; infection by a virus; injuries from alkalis, fertilizers, air pollution or cold; insect, mite, or nematode feeding; main gas leaks; compaction or change in soil level; and stem or root rot.

Symptoms can occur on a few leaves, on one or two branches, half of the tree or the entire plant. The first indication of chlorosis is a paling of the green color of the foliage, followed later by a general yellowing. If the disease continues to progress, the tissue between the leaf veins turns bright yellow.

In advanced cases, leaf size is stunted and the leaf tissue is pale white to pale yellow. The leaf margins may become scorched or develop brown, angular spots between the veins, and the leaves may wither and drop prematurely.  Severely chlorotic plants are stunted, and shoots may die back to the roots.

Chlorosis that persists year after year may lead to the death of individual branches or the entire tree.