Exanthema in citrus' tress is a reserves of the deficiency of

Exanthema in citrus trees is a reserve of the deficiency of Copper.
The branches, especially the terminal ones, the leaves, and the fruit are all attacked. As a general rule, there is no apparent effect on the roots. The symptoms of exanthema are variable. Severely affected trees carry a large quantity of dead wood.
The dropping, blemishing and cracking- of fruit form one of the most common symptoms. Brown glossy areas occur particularly on one side of the fruit. The surface may show small dots of gum.
Copper treatment may take two forms. The trees may be sprayed with a weak Bordeaux mixture, preferably at blossoming time.