CITRUS MELANOSE AND ITS CONTROL 
23 
ble parts are moist for 20 hours or more. This is corroborated by 
general field observations as well as by the results presented in 
Table 2. 
Another series was run to determine the effect of various tempera- 
tures upon the infecting power of spores of Phomopsis citri in sus- 
pension. Spore suspensions were held at 10°, 20°, and 30° C, respec- 
tively, and inoculations were made under natural conditions of 
temperature at the expiration of 8, 24, 32, 48, 72, and 96 hours, 
respectively. Inoculum held at 10° C. caused infections that for 
the most part were of a slight degree; that held at 20° caused infec- 
tion ranging from slight to very severe, averaging a medium degree ; 
and that held at 30° produced 100 per cent infection, ranging from 
very slight to very severe, averaging slight. Invariably the lightest 
infection occurred on plants that were inoculated with spore suspen- 
sions 72 hours old or older, whereas the heaviest infection developed 
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£& SO 32 3+ 3S 30 *<? 
Fig. 3.— Percentage of grapefruit leaves developing melanose infection after being 
inoculated and held for 40 days at various maintained temperatures from 10° 
to 30° C. The average intensity of infection for each set of plants is indicated 
as varying fromi very slight to severe 
from inoculum held 24 hours or less. For checks the plants were 
inoculated with fresh inoculum that resulted in very severe infection. 
Still another series was run in which the plants were inoculated 
with fresh viable spores; placed in compartments at 10°, 15°, and 
20° C. ; left there for 16, 24, 40, 48, 72, 96, 120, 144, and 168 hours, 
respectively; removed and placed in the summer sun for two hours, 
where they dried before being returned to the same compartments 
without being washed with a disinfectant. On all plants irrespective 
of temperature the degree of infection ranged from medium to very 
severe, and infection of like intensity developed on the check plants 
which were not sunned. These findings seem to indicate that a short 
sun exposure has little or no effect upon melanose infection when 
such exposure occurs as much as 16 hours after inoculation. 
