Bulletin 229, Diseases of Citrus in Florida


reduction of the amount of stem-end rot that may be expected
to develop in the fruit during marketing. This reduction may
be as high as 50 percent from a single application that produces
satisfactory results in the control of melanose. The other is the
reduction in the tendency of the fruit to develop the symptoms
of exanthema known as ammoniationn". Spraying with bor-
deaux mixture or bordeaux-oil emulsion will completely elimi-
nate this trouble in many instances. A marked beneficial effect
commonly occurs also in the trees themselves that may be suf-
fering from exanthema diebackk).

 SCAB
 Caused by Sphaceloma fawcettii Jenkins
 Citrus scab, lemon scab, sour scab, or verrucosis, as the dis-
ease has been variously termed, is widely distributed through-
out Florida and the Gulf States, where it causes serious injury
to a number of species and varieties of citrus fruits. This dis-
ease appears to have been unknown in the United States until
about 1885, when it was discovered near Ocala, Florida, on sour
orange nursery stock. It is believed to have been introduced into
this country on Satsuma orange trees from Japan, where it has
been present from ancient times. It was reported on lemon trees
in Florida in 1886 and gradually spread to all citrus-growing
sections of Florida and, later, to the Gulf States. Scab early
assumed commercial importance in Florida in disfiguring lemon
fruits and it was the pronounced susceptibility of the lemon to
both scab and cold that resulted in the general abandonment of
its commercial culture before 1910 in this state. Scab has now
spread to many citrus-growing countries of the world where the
moisture and temperature conditions are favorable to its de-
velopment.
 Scab may attack, to a greater or less extent, the leaves, twigs
and fruits of many kinds of Citrus. Within a given species,
certain varieties may be very susceptible to the disease while
others are practically immune. Among the commercial species
and varieties grown in Florida the sour orange, lemon, and
some of the tangelos are extremely susceptible. The grapefruit
and shaddock are quite susceptible to infection, as are also the
King orange, Temple orange, mandarin orange, and Satsuma