Bulletin 229, Diseases of Citrus in Florida


branches, should be treated with some good antiseptic and water-
proof wound dressing to prevent the drying out of the wood, in-
fection by organisms causing gumming and other diseases, and
invasion by ants and other woodboring insects. It is very im-
portant to protect with whitewash the trunks and branches fully
exposed to the sun, so as to prevent the destructive action of sun-
scald. Care and attention devoted to the proper pruning and
treatment of wounds and protection from sunscald will be repaid
a thousandfold in the future welfare of the trees.
 If weather conditions continue favorable and growers exercise
proper care and good judgment in fertilizing and cultivating, a
large percentage of the frost-injured trees will recover; other-
wise, many will develop mottle-leaf, withertip, gummosis, or
other troubles and decline to the point where they may have to
be taken out. Special effort should be made to maintain an ade-
quate supply of moisture in the soil during the spring drought.
 SUNSCALD

 Sunscald frequently occurs on citrus foliage and fruits and,
 occasionally, on the exposed trunks and larger branches. It is
 an injury attributable to the combined action of heat and light
 resulting from direct exposure to the sun.
 On the Leaves:-Sunscald is more common on the under sur-
 faces of leaves that have suddenly become exposed for a time
 to the direct rays of the sun. It occurs commonly after a flush
 of growth has developed and before the leaves have hardened,
 especially when wind or rain has beaten the foliage about and
 left the under surfaces of the leaves exposed to the hot sun. The
 symptoms of the trouble vary greatly according to the amount of
 leaf surface turned over and the severity of the injury. The
 most common symptom is the occurrence of numerous raised,
 hard, glazed spots, which may vary in size from mere specks to
 patches covering a considerable area of the leaf. The epidermis
 between these hard, glazed spots has a more or less silvery ap-
 pearance on the portion of the leaf that was turned over. In
 other cases merely a reddish-brown stain is produced on the
 portion of the leaf surface affected. From only a small part of a
 leaf to as much as two-thirds or more of its entire surface may
 be involved, depending upon how much of the leaf was turned
 over (Fig. 85). The injury is of minor importance on the foli-
 age.