Florida Agricultural Experiment Station


orange, which belong to the mandarin group of oranges. The
sweet or round oranges are rarely attacked and may be con-
sidered quite resistant. The Mexican or Key lime, kumquat,
citron and Cleopatra mandarin are apparently immune.
 The greatest commercial injury caused by scab is to the grape-
fruit crop. It is owing to the large increase in grapefruit plant-
ings that this disease has attracted more attention in recent
years than formerly in Florida. All varieties of grapefruit,
however, are not attacked to the same degree. According to
Hume, the Hall is the most susceptible variety, while Marsh is
the least susceptible. He states that Duncan, Walters, and Fos-
ter are less affected than Hall. According to Winston, the Royal
and Triumph grapefruits (supposed to be hybrids of orange and
grapefruit) appear to be immune.
 In general importance as a source of loss to the Florida citrus
industry, scab is probably surpassed only by such diseases as
melanose, blue and green mold decays, and stem-end rot. Scab
is not uniformly serious throughout the citrus-growing sections
of Florida, but may be of the greatest importance in certain well-
defined localities, especially in the interior of the peninsula. The
losses occasioned by this disease result primarily from heavy
premature dropping of young fruit and a marked reduction in
the grade of the fruit that reaches maturity, much of which is
rated as culls. In severe attacks of the disease, from 50 to 90
percent of the fruit of susceptible varieties in an affected grove
may be injured. Winston states that an average estimate of the
scab losses to Florida growers, made by conservative business
men familiar with the citrus industry, is about 1,000,000 boxes
of fruit annually. This means a considerable increase in the
cost of producing grapefruit, tangerines, mandarin oranges,
tangelos, and lemons of first quality in districts where scab is
a serious factor and has to be controlled by spraying.
 With the exception of damping-off of seedlings, scab is the
only parasitic disease of consequence occurring in the citrus
nursery. There it is extremely serious and produces a marked
stunting effect upon seedling stocks of sour orange and rough
lemon for budding, frequently reducing the growth from 40 to
50 percent.
 SYMPTOMS OF SCAB
 Scab occurs on the leaves, twigs and fruits of susceptible spe-
cies and varieties of Citrus. These parts are attacked only while