Bulletin 229, Diseases of Citrus in Florida


 CAUSE OF SCAB
 Scab is caused by a microscopic, parasitic fungus which fruits
on the surfaces of the scabby outgrowths. The fungus was first
isolated by Fawcett in 1906, who incorrectly assumed it to be
Cladosporium citri Massee. It has recently been placed in the
form genus Sphaceloma by Jenkins, who made a critical study
of it and named it Sphaceloma fawcettii in 1925.
 The causal fungus lives over the winter period on the attacked









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 Fig. 10.-Grapefruit severely affected with scab.

leaves and twigs, which serve as sources of infection the follow-
ing spring. Winston concluded from cultural data and field ob-
servations that the disease is seldom, if ever, carried over winter
on fruit set in the spring or summer. It is disseminated by
such agencies as wind, rain, dripping of water from dews and
fogs, and by insects. The disseminated spores are capable of
infecting the tissues of susceptible species and varieties of Citrus