60 BULLETIN 1474, U. S. DEPARTMENT OF AGRICULTURE 
Florida is to place the requisite quantity (12 pounds for 200 gallons 
of spray) of finely pulverized bluestone in a suitable strainer in the 
opening of the spray tank. This will dissolve as the tank is filled. 
When nearly full, start the agitator and sift in 16 pounds of builders' 
hydrated lime (taking the place of 12 pounds of quicklime usually 
specified). Last of all add 3 gallons of oil emulsion while the 
agitator is kept running. 
EXTRA SPRAYS FOLLOWING MELANOSE APPLICATION 
Spraying with any material that will effectively prevent melanose 
infection will very likely be about equally disastrous to the fungi 
parasitic upon citrus insects, thereby resulting in a considerable and 
usually rapid increase in scale insects. Experience has shown that 
wherever simple copper sprays are applied, or even combinations of 
such sprays with oil emulsion, during spring months, a follow-up 
spray of oil emulsion should be made to prevent serious damage 
from these pests. The Bordeaux-oil emulsion in April or early May 
is not only effective against melanose but also controls the white flies 
as well. Nevertheless when this spray is applied an oil emulsion of 
high efficiency should be applied in late June or early July while 
the scales are in an immature state. Sometimes this extra oil spray 
may be delayed until fall, but such delay is not safe and may lead to 
considerable damage from scale insects during the summer. 
SUMMARY 
Melanose, a fungus disease caused by PKorrwpsis citri Fawcett, at- 
tacks a wide range of rutaceous plants including all citrus forms 
grown commercially in Florida. This organism is also the cause of 
a stem-end rot that occurs in large proportions on Florida citrus 
fruits. 
Pkomopsis citri sporulates in nature only in dead bark of twigs 
and limbs ; it has never been observed in or cultured from melanose 
lesions on living parts. Spore production, germination, infection, 
and incubation are markedly retarded by temperatures either above 
or below the apparently optimum range of from 68° to 81.5° F. (20° 
to 27.5° C). Infection may take place at any time of the year when 
rainy periods occur while growing parts are in a susceptible stage. 
Leaves of the orange and grapefruit are susceptible to infection 
from the time they emerge from the bud until they become distinctly 
tough; this usually requires about two or three weeks. The fruits 
of the orange and grapefruit are at first very susceptible to infection. 
They become progressively resistant with increasing size; oranges 
develop practical immunity when they reach about V/ 2 inches in 
diameter, whereas grapefruits do not become practically immune 
until they reach about %y 2 inches in diameter. 
Under Florida conditions, oranges and grapefruits from February 
or March bloom become practically immune in May ; seldom are they 
susceptible to infection after June 10. 
Priming away the dead and weakened parts, thereby removing the 
source of infection, has not proved to be a dependable means of 
preventing melanose outbreaks under ordinary commercial condi- 
