Florida Agricultural Experiment Station


 dinarily, the leaves are susceptible to infection for from two
 to three weeks in periods of good growing weather. Melanose
 infection of the leafy parts of the tree, however, ordinarily is
 not of sufficient economic importance to justify special control
 measures.
 The fruits are likewise very susceptible to infection when
 first formed but become progressively resistant with increasing
 age. The approximate size at which they develop practical im-
 munity from mel-
 anose, based on
 diameter m e a s-
 urements, varies
 from an inch for
 p: n llF tangerines, 11/2
 Inches for or-
 ,. I anges, and 21/2
 inches for grape-
 a e fruit.
 The severe
 outbreaks of mel-
 anose can be
 Sr l traced definitely
 Sto rainy periods
 .. occurring as a
 rule in May or
 l' c l early June after
 Fig. 6.-Melanose on grapefruit, showing tear- the melanose
 streaked effect.
 spores have had
 a chance to develop in abundance and before the young fruits
 have had a chance to outgrow the susceptible stage. The sud-
 den showers, heavy dews and fogs that come earlier do not ap-
 pear nearly so favorable for infection as do cloudy, rainy periods
 of two or three days' duration. The rainy periods that com-
 monly occur late in March come well after most of the spring
 flush of growth has hardened but long before even the fruit from
 the earliest bloom has become resistant and sometimes before
 much of the bloom has set fruit. While a moderate amount of
 fruit infection almost invariably takes place when these March
 rains occur, ordinarily, the principal infections do not occur be-
fore the latter part of April or early May, since April usually
is one of the driest months of the year.