CITRUS MELANOSE AND ITS CONTROL 17 
Viewed over a period of eight years' observation and study, it 
seems apparent that dew drip and rain drip or rain spatter from 
dead parts in the tree are the important means of dissemination of 
the causal organism. 
CONDITIONS FAVORING INFECTION 
Melanose infections are likely to occur in Florida at any season 
of the year when rainy periods coincide with the time when leaves, 
twigs, or fruits are in a susceptible condition. Scattering citrus- 
melanose scars have been observed on several occasions on flushes of 
growth developing in winter and repeatedly on those expanding in 
early spring, but for all practical purposes melanose is not likely 
to occur in quantity on the early spring flush. Almost every year 
rainy periods occur in March well after most of the spring vegeta- 
tive flush has hardened, but long before the fruit has become resist- 
ant. When these March rains occur a moderate amount of fruit 
and flower infection (pi. 1, C) almost invariably takes place, but 
ordinarily the principal infections seldom occur before May, April 
being one of the driest months of the year. Along with the May 
rains come severe melanose outbreaks on the fruit, followed by 
later outbreaks on the second flush. Fruit setting in May or June 
is very likely to have melanose markings, although as a general rule 
spring-bloom fruit in central Florida has melanose worse than sum- 
mer-bloom fruit. The vegetative flush which expands in late summer 
or early fall is in general more severely blemished by this disease 
than any other growth. 
Melanose outbreaks vary from season to season and from locality 
to locality, not only in the cumulative severity of the disease for the 
season, but also in the severity of the onset of the disease. In certain 
years the heaviest infections may occur at the very beginning of the 
rainy periods, especially if the rains continue for 36 to 48 hours 
without enough interruption to permit the tree to dry off completely. 
At other times they do not take place until weather conditions have 
been apparently favorable for infection for 10 da}^s or two weeks. 
Ordinarily melanose infection on leaves and twigs does not occur 
in sufficient proportions to justify special protective measures; how- 
ever, occasionally there are notable and extreme exceptions. These 
exceptions have been repeatedly observed in groves receiving good 
care and frequent pruning, as well as in indifferently cared for 
properties. 
Although outbreaks of citrus melanose appear to be erratic, they 
are far more uniform than citrus scab, and it frequently happens that 
within a given locality of a dozen or more groves, all receiving essen- 
tially the same care and with approximately the same topography, 
citrus-melanose outbreaks vary from slight to very severe. It some- 
times happens that general grove practices, exclusive of spraying 
operations, that are intended to keep trees in a vigorous condition and 
commercially free of deadwood seem actually to promote melanose 
outbreaks. This has been noted in a number of groves or portions of 
groves which received several prunings irrespective of whether only 
24975°— 27 2 
