34 BULLETIN" 1118, U. S. DEPARTMENT OF AGRICULTURE. 



The spray schedules shown in Table 11 are drawn to meet the 

 varying degrees of citrus-scab outbreaks as they occur in Florida 

 orchards. Spray schedule No. 1 should be followed where scab is 

 usually present in serious proportions; spray schedule No. 2 should 

 be followed in localities where citrus scab varies in prevalence from 

 serious to moderate; spray schedule No. 3 should be followed in 

 localities where citrus scab is a minor disease. Because of its effect 

 upon spiders, mites, and insects, schedule No. 3 wUl prove profitable 

 even if citrus scab does not occur on unsprayed trees. 



Nurseries can be kept commercially free from citrus scab by occa- 

 sional apphcations of Bordeaux mixture plus oil emulsion. On an 

 average, monthly applications probably wiU afford adequate protec- 

 tion. In many instances a smaller number of applications will 

 suffice; however, the frequency of applications is dependent upon 

 local and seasonal conditions. Care must be taken to keep new 

 flushes protected during periods of wet weather. 



The use of Bordeaux mixture plus oil emulsion was followed by a 

 considerable increase in the growth of grapefruit seedlings even when 

 citrus scab jdid not occur in the planting. Where citrus scab has 

 occurred on sour-orange and rough-lemon seedlings the increase of 

 growth f oUowing apphcations of Bordeaux mixture plus oil emulsion 

 has been greater than the probable retardation due to scab. These 

 two observations seem to indicate that this spray mixture may act as 

 a growth stimulus in citrus nurseries. 



SUMMARY. 



Citrus scab, an important disease of foreign introduction, attacks 

 many citrus species. It occurs in India, China, Formosa, Japan, 

 Hawaii, Paraguay, Brazil, Canal Zone, Yucatan, West Indies, Canary 

 Islands, South Africa, and the citrus-growing regions of the Gulf States. 

 As yet it has not become established in California or Arizona. 



This disease is second in importance to melanose and stem-end 

 rot caused by PTiomopsis citri. It is the most serious fungus disease 

 of the citrus nursery, where it attacks leaves and succulent twigs. 

 In the orchard its activity is mainly confined to fruit and leaves. 



Leaves are most susceptible in the very early stages of growth. 

 They become entirely resistant by the time they reach half an inch 

 in width. 



Young grapefruits are extremely susceptible to infection immedi- 

 ately after the faUing of the petals. They become progressively 

 resistant until they reach immunity at a diameter of about three- 

 fourths of an inch. 



Scab infections are likely to occur whenever there is sufficient 

 moisture at the time the parts are in a susceptible stage. Under such 

 conditions infections developing in the hot, rainy summer months 



