CITRUS scab: its cause and control. 35 



are as severe as those occurring during the cool weather of spring or 

 faU. 



Citrus scab is caused by a definite fungus usually but erroneously 

 referred to as Oladosporium citri Massee. It has none of the charac- 

 ters of Oladosporium Link. It has been confused with a common 

 saprophyte in citrus lesions. 



The causal fungus does not live over winter on mature fruit. It 

 passes this period on affected leaves which act as foci of infection the 

 following spring. 



The citrus-scab fungus does not appear to be more virulent now 

 than was the case a few years after its first introduction into America, 

 nor are the various citrus varieties changing their former suscepti- 

 bility. 



There is no material difference in percentage or degree of infection 

 that could reasonably be attributed to immunizing or sensitizing in- 

 fluences produced by the root stock on the scion. 



Cumulative evidence including spraying experiments and orchard 

 observations, goes to show that citrus scab can be controlled satisfac- 

 torily and economicaUy. Scab in the nursery can be controlled 

 readily by occasional apphcations of effective sprays. 



Plain Bordeaux mixture as well as Bordeaux mixture plus oil 

 emulsion is very effective against citrus scab, either in the nursery or 

 in the orchard. Burgundy mixture is distinctly less effective than 

 Bordeaux mixture, and ammonical copper carbonate solution is much 

 less so. 



Lime-sulphur solution is much less effective against this disease 

 than is Bordeaux mixture. The other sulphur sprays are no more 

 effective against citrus scab than is lime-sulphur solution. 



Spraying after the smallest fruits have attained a diameter of 

 three-fourths of an inch has no effect on the control of scab. 



