16 BULLETIN 1414, tT. S. DEPARTMENT OF AGRICULTURE 
ones become more plainly visible. In the meanwhile, apparently 
another crop of pycnidia develops rapidly, and in a few weeks begins 
discharging spores in large numbers. 
This succession of crops continues indefinitely, but under ordinary 
conditions these fruiting bodies do not appear to be quite as numerous 
in midsummer or late summer as in the spring or fall. 
Usually a number of saprophytic fungi develop in dead bark along 
with Phomopsis citri. Among these, Colletotrichum, Diplodia, and 
Phoma species are most frequently observed. 
DISSEMINATION OF THE CAUSAL ORGANISM 
From the general structure of the fruiting body and the periods 
of normal spore discharge, together with the localization of the 
disease with respect to foci of infection, it would seem that Phomop- 
sis citri is disseminated principally through rain drip, rain spatter, 
driving rain, or dew drip. Spore emergence is plainly visible in 
rainy periods, but in dry weather it is not apparent, if it occurs at all. 
The relative absence of melanose from the tops of trees, as well as 
from the outermost parts that are not subjected to trickling or spat- 
tering water from infected twigs above, and the great abundance of 
melanose within the head of the tree and on those outer parts that are 
wet with drippings from dead parts above (pi. 9, C) are strong evi- 
dence that the causal organism is water borne. Except in periods of 
hurricanes and gales there is little or nothing to suggest that spore- 
laden water is blown any great distance. This is indicated by the fact 
that in mixed plantings of old, melanose-harboring trees with young 
resets melanose normally occurs in abundance on the old trees and to 
a considerable degree on the young trees within 15 to 20 feet of the 
source of infection, but the young trees 30 or more feet away seldom 
have melanose markings. 
Insects are doubtless capable of accidentally transporting spores 
of the causal organism, but no evidence has been found to indicate 
that such animals are importantly concerned in disseminating 
P. citri. This may be accounted for in a measure by the fact that 
spore-bearing parts of the host seldom attract the common insects 
of a citrus grove. 
In order to determine whether primings on the ground are a 
source of melanose infection, prunings of dead or weakened twigs 
and limbs were left under trees throughout the season of infection, 
and although the melanose fungus may develop abundantly on these 
pruned parts, no appreciable increase in melanose was observed on 
these trees in excess of what developed on pruned trees from which 
the prunings were hauled away. Even those tender parts within 
a foot or less above piles of prunings failed to develop melanose in 
greater quantity than similarly situated parts on check trees. This 
test was conducted over a period of three years. 
Attempts have been made repeatedly to trap spores in Petri dishes 
from air currents during fair weather and occasionally during in- 
clement periods. The traps were placed at regular stations in old 
seedling plantings where there was an abundance of melanose, and 
exposures were made for varying lengths of time at intervals 
throughout the day and season. In no case were viable Phomopsis 
spores trapped. 
