Florida Agricultural Experiment Station


 BLACK ROT
 Caused by Alternaria citri Ellis & Pierce
 Black rot of oranges is widely distributed throughout the
 citrus region of Florida but it is only in occasional years that the
 disease becomes sufficiently prevalent to cause considerable dam-
 age. Such was the case in 1911 and 1922.
 This disease was first described in 1901 by Pierce, who noted
 it occurring in California as early as 1892. The same or similar
 decays of oranges have also been reported to occur in Arizona,
 Cuba, South Africa, and in Victoria, Australia.
 It was formerly thought that attacks of black rot were con-
 fined to the navel orange but the disease has long been known
 to attack other varieties. In Florida, the occurrence of this de-
 cay was reported on Pineapple and Ruby Blood oranges by Faw-
 cett in 1911, and on Jaffa, Parson Brown, Pineapple, Ruby Blood,
 and Valencia oranges, and on tangerines by Burger in 1922.
 Field observations by Burger during the middle of November
 of this year, following unusually wet weather, showed that black
 rot infection in some groves involved from 5 to 25 percent of the
 orange crop. One grove of Jaffa oranges was visited in which
 25 percent of the fruit had dropped because of black rot infec-
 tion and undoubtedly a larger percentage eventually developed
 the disease.
 SYMPTOMS OF BLACK ROT
 The most characteristic external symptom of black rot on
oranges is the premature coloring of full-sized or nearly full-
sized fruit. The disease is most conspicuous just before the
normal crop colors. At this time the infected fruits color sooner
than the remaining sound fruits and turn a deep-orange color.
Many of the diseased oranges fall from the trees early in the sea-
son, while others which were perhaps infected later or in which
there has been a very limited development of the causal fungus
remain on the trees. Such fruits often look sound on the exterior
but, when cut, have a dry, black decayed place within, at, or
near the stylar end.
 Black rot begins at the stylar, or so-called "blossom", end of
the fruit. The causal fungus seems to make but a weak attack
upon the tissues of the fruit and has very limited power to
spread, working mainly along the core. The rind is not affected
at first and becomes involved only after the fungus has made