citrus scab: its cause and control. / 
Bordeaux mixture gave satisfactory control (25) and sulphur dusts 
no control of this disease. 
Grossenbacher (7) lists susceptible species in Florida and discusses 
conditions favoring citrus-scab outbreaks. His attempts to pro- 
duce the disease artificially failed, undoubtedly because he used cul- 
tures of the saprophytic Cladosporium sp. which develops on old 
citrus-scab lesions rather than the active pathogen first isolated by 
Fawcett. Bordeaux mixture proved to be much more effective than 
lime-sulphur solution against citrus scab. Spraying after the middle 
of May was found to be too late for effective citrus-scab control. He 
advises one application of Bordeaux mixture in the height of the 
bloom, followed in a week or 10 days by an application of lime-sul- 
phur solution and still another application of lime-sulphur solution 
two or three weeks later. 
Fawcett (5) reports further confirmative inoculation experiments 
in producing typical scab lesions by using the true scab organism. 
He further discusses the confusion of this organism with the common 
saprophytic Cladosporium. 
Lee (11) reports finding citrus-scab lesions on leaves of Citrus 
nobilis collected by Maximo wicz in 1863 at Nagasaki and deposited 
in the herbarium of the Hongkong Botanic Gardens. This observa- 
tion coupled with the fact that scab is distributed throughout the 
citrus-growing section of South China led him to conclude that this 
disease may be indigenous to the Orient. 
Stevens (22) found in avocado-scab lesions an organism in every 
morphological and cultural character similar to the citrus-scab 
fungus. With the avocado-scab fungus he produced typical scab 
lesions on the avocado as well as on the citrus, but the fungus isolated 
from lesions on citrus failed to infect the avocado. In a later publi- 
cation (23) he predicts that scab will eventually be as severe on the 
round orange as it is now on the grapefruit. 
Fawcett (6) reports the results of experiments to determine the 
effect of constant temperatures on infection of sour-orange leaves 
and on the vegetative growth and spore development of the citrus- 
scab fungus. Infection on rapidly growing parts occurred between 
16° and 23° C, while detached leaves floated in water were infected 
at temperature ranging from 16° to 27.5° C. Vegetative growth was 
most rapid at 21° C. Spores developed at all temperatures from 
13.5° to 27.5° but not at 32° C. At 21° C. the spore development 
was more abundant than at lower or higher temperatures. In the 
light of these experiments Fawcett thinks the relatively low tem- 
peratures of spring tend to aid and the high temperatures of summer 
in Florida to retard or inhibit infection. 
