Bulletin 229, Diseases of Citrus in Florida


these diseases and to make applications of fungicides and the fol-
low-up spray of oil emulsion at the correct time.
 The effectiveness of any control measure will depend upon a
proper, intelligent and timely use of the information- given.
Thoroughness is most essential, since very little good will be
accomplished if control measures are applied carelessly or in-
differently. The control of many diseases, such as melanose and
scab for example, must be effected by preventive measures before
the susceptible parts become infected. Even in the case of other
diseases and injuries, however, it will be found easier and less
expensive to prevent their occurrence than to control them after
they develop. This is especially true in starting with a new
grove.
 SPRAYING

 While spraying operations in the citrus grove are performed
most frequently for the control of insect pests, it is often neces-
sary to spray for the control of certain fungus diseases such as
melanose and scab, which attack the foliage, twigs and fruit.
A fungicide is used for the latter purpose and is applied at in-
tervals to protect any exposed surfaces during the period when
these tissues are susceptible to attack by a disease. The control
of fungous diseases of citrus trees is very intimately tied up with
the control of insect pests, however, and, in many cases, the
two are controlled simultaneously by a combination spray of
bordeaux-oil emulsion, in which the bordeaux mixture is the
fungicide and the oil emulsion the insecticide.
 Citrus trees are more difficult to treat successfully with fun-
 gicides and insecticides than deciduous fruit trees, since they are
 evergreen and retain their foliage throughout and put out new
 growth at several times during the year. Moreover, the trees
 are frequently allowed to carry their fruit the greater part of
 the year. Thus, there is no dormant period when the leaves,
 and often the fruit, are absent, which would permit the use of
 a strong fungicide or insecticide.
 The greatest difficulty involved in the use of fungicides on
 citrus trees, however, arises from the indirect effect that they
 have on the increase of insect pests. When used at the proper
 strength, fungicides kill all fungi with which they come in con-
 tact; hence the beneficial (entomogenous) fungi are also killed,
 thereby allowing the scales and whiteflies to increase rapidly.