UNITED STATES DEPARTMENT OF AGRICULTURE 



^■f BULLETIN No. 1118 fMf 



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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 of 



Plant Industry. 



CONTENTS. 



Page. 

 Economic importance and distribulion of 



citrus scab l 



Species and varieties attacked 3 



Description of tlie disease 3 



Review of the literature 5 



The causal organism 8 



Pathological anatomy 12 



Dissemination of the causal fimgus 12 



Conditions influencing infection 13 



Growth habits of grapefruit 



Disease as influenced by tlie stock . 



A daptation of the fungus 



Inoculation experiments 



Sprajdng experiments 



Commercial control 



Summary 



Literature cited 



20 



21 

 21 

 22 

 27 

 30 

 34 

 37 



ECONOMIC IMPORTANCE AND DISTRIBUTION OF CITRUS SCAB. 



Citrus scab, or verrucosis (also commonly known as lemon scab, 

 sour-orange scab, soiu* 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°— 23— Bull. 1118 1 1 



