FLORIDA STATE HORTICULTURAL SOCIETY. 
85 
pears to be one of those minor troubles 
that come and go. Some years it is quite 
bad, while other years it is scarcely at all 
noticeable. We are now making a study 
of this disease. 
scab. 
Scab is a disease which is ordinarily 
of rather minor importance, but which 
may at times break out upon young 
leaves and fruits of lemons, grapefruit 
and satsumas, in a very destructive way. 
It is sometimes known as “sour scab,” 
because it is so invariably found upon 
sour oranges and lemons. It is probably 
found on sour oranges in almost every 
citrus-growing district in the State. 
The earliest infections are on young 
leaves about one-tenth full size, as mi¬ 
nute, light-brown or cork-colored points. 
Soon the spots become depressed on one 
side of the leaf and raised on the other. 
Older spots become dark brown and 
sometimes pinkish in color. The sep¬ 
arate spots coalesce as they enlarge, form¬ 
ing irregular corky scabs. The leaves 
are contorted, twisted and warped. The 
fruit, when affected, presents a warty 
appearance. 
The disease is caused by a minute fun¬ 
gus (Cladosporium citri) that grows into 
the tissue of the leaves. The spores of 
this fungus are so small that it would 
take about 8,000 side by side to measure 
one inch. Pure growths of the scab fun¬ 
gus were obtained in a nutrient jelly by 
sowing some of these minute spores, and 
a study was made of the fungus as it 
grew on this jelly. When the fungus had 
grown sufficiently to produce a good crop 
of spores, these were sprayed on to small 
sour orange trees that were in the green¬ 
house and were free from scab. In a 
few days the characteristic scab spots ap¬ 
peared, proving that this fungus was the 
real cause of scab, and that the infection 
came from the growth of the spores that 
had been put upon the surface of the 
leaves. 
Treatment —Sometimes the disease 
breaks out early in the year, on quite 
young leaves and fruits, and in a very 
severe form. The only known preven¬ 
tive of its spread is Bordeaux mixture 
applied early in the year. The same care 
should be used in applying the Bordeaux 
as when spraying to cure withertip, or 
its application will be followed by an in¬ 
crease of scale insects. 
SMOKY FUNGUS. 
The smoky appearance of the orange 
caused by the smoky fungus (Leptothy- 
rium pomi?) is not to be confused with 
the blackening due to the sooty mold 
which accompanies the whitefly. The 
smoky fungus may occur when the white- 
fly is absent. It causes no noticeable in¬ 
jury to the fruit itself. It does, however, 
mask the bright color of the fruit by a 
layer of dark-colored, mycelial threads, 
which spread over the surface of the 
rind. It may be rubbed off with the fin¬ 
gers, and so is attributed by some growers 
to the accumulation of dust from the air. 
It is most apt to occur in moist groves, 
late in the fall, and on oranges that have 
remained on the tree after they are ripe. 
The selling quality of the fruit is natur¬ 
ally somewhat impaired by the presence 
of this fungus. 
Remedies —>(i.) The smokiness may 
be readily removed from the fruit by 
putting it through a washer like those 
