UNITED STATES DEPARTMENT OF AGRICULTURE 
H BULLETIN No. 1118 Jl 
jf^^"^3L 
Washington, D. C. 
PROFESSIONAL PAPER 
January 26, 1923 
CITRUS SCAB: ITS CAUSE AND CONTROL. 
By John R. Winston, Pathologist, Office of Fruit-Disease Investigations, Bureau f 
Plant Industry. 
CONTENTS. 
Page. 
Economic importance and distribution of 
citrus scab 1 
Species and varieties attacked 3 
Description of the disease 3 
Review of the literature 5 
The causal organism 8 
Pathological anatomy 12 
Dissemination of the causal fungus 12 
Conditions influencing infection 13 
Page. 
Growth habits of grapefruit 20 
Disease as influenced by the stock 21 
Adaptation of the fungus 21 
Inoculation experiments 22 
Spraying experiment^ 27 
Commercial control 30 
Summary 34 
Literature cited 37 
ECONOMIC IMPORTANCE AND DISTRIBUTION OF CITRUS SCAB. 
Citrus scab, or verrucosis (also commonly known as lemon scab, 
sour-orange scab, sour scab, and grapefruit scab), is a parasitic 
fungous disease of the twigs, leaves, and fruits of many species 
of citrus. 
Citrus scab occurs in India, South China, Formosa, Japan, Hawaii, 
Paraguay, Brazil, Canal Zone, Yucatan, Texas, Louisiana, Missis- 
sippi, Alabama, Florida, Cuba, Isle of Pines, Porto Rico, and the 
lesser islands of the West Indies. It is also reported as being in 
the Canary Islands and the Union of South Africa. 
In general importance to the citrus industry, citrus scab is second 
only to the diseases known as melanose and stem-end rot, caused 
by Phomopsis citri Fawcett. It was largely responsible for the 
failure of the lemon industry in Florida, which prior to the intro- 
duction of citrus scab gave promise of becoming a very profitable 
undertaking. 
Throughout the Gulf and South Atlantic regions, wherever citrus 
fruits are grown, as well as in Cuba, Porto Rico, and the less im- 
portant citrus districts in the Caribbean Sea, citrus scab has already 
become very firmly established and doubtless will increase in im- 
portance, especially in those localities where the grapefruit industry 
4573°— 33 —Bull. 1118 1 1 
