Bulletin 229, Diseases of Citrus in Florida


scald of fruit is usually most prevalent on the outer and unpro-
tected fruit on the southwest sides of trees. It starts as a pre-
mature yellowing of that portion of the surface of the fruit that
is most fully exposed to the sun. In the milder cases of burning
the surface becomes pitted from the drying of the oil cells (Fig.
86, left). In the more pronounced cases of sunscald the cells of
the rind may be so severely injured that the affected spot may
develop a hard, grayish to blackish, scabby, callus tissue (Fig.
86, right). The burned spots vary from 3/ to 11/ inches in di-
ameter. The affected spot is dry to the touch and holds the heat
in contrast to unaffected portions of the fruit. This type of in-
jury generally disfigures the fruit to the extent that it becomes
a cull. Sunscald commonly results in the loss of considerable
fruit. King oranges are especially subject to this trouble.













Fig. 87.-Long area of bark killed by scalding on nearly horizontal citrus
 limb exposed to the direct rays of the sun.

 On the Trunks and Limbs:-The bark of citrus trees is very
 susceptible to injury from sunscald and a few days' exposure to
 the hot sun may be sufficient to cause irreparable injury to
 the trunk and limbs that have been accustomed to shade. Pro-
 tecting the trees against sunscald, therefore, is a matter of
 great importance to the citrus grower.
 Severe sunscald of the bark is most likely to develop as a re-
 sult of exposure of the trunks or main limbs where a portion of
 the tree crown has died back following such injuries as freezing,
 disease, water injury, or dehorning. This is especially true of
 trunks and branches that have been accustomed to shade. Young
 trees set out during hot weather are very liable to be injured by
 sunscald. Sunscald is often a factor of considerable importance