But unlike magnesium deficiency, manganese deficiency symptoms seldom develop so far as to produce interveinal chlorosis, the chlorosis normally being confined to leaf margins. The other distinguishing characteristic is that manganese deficiencies appear on the youngest leaves first, and the finest leaf veins do not remain green as they do with iron deficiencies. It is caused in part by an excess of manganese accompanied by low calcium levels. In most fruit crops, boron deficiencies show up in the fruit before appearing in the leaves. This symptom is often confused with bitter pit or corking caused by calcium deficiency.
Researchers disagree whether the two symptoms can be told apart visually.
Boron deficiency might be distinguished from bitter pit by the presence of pitting from the peel to the core, whereas in bitter pit the pitting usually occurs only at the calyx end and only very close to the skin. In some instances of boron deficiency, the entire surface is covered with cracks that have callused over, producing a russeted appearance. In plums, the symptoms appear as brown sunken areas in the fruit flesh, ranging in size from small spots to almost the whole fruit. The fruit usually colors earlier than normal, and falls. Gum pockets may also form in the flesh.