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 will prove profitable 
even if citrus scab does not occur on unsprayed trees. 
Nurseries can be kept commercially free from citrus scab by occa- 
sional applications of Bordeaux mixture plus oil emulsion. On an 
average, monthly applications probably will 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 did not occur in the planting. Where citrus scab has 
occurred on sour-orange and rough-lemon seedlings the increase of 
growth following applications 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 Phomopsis 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 falling 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 
