98 
FLORIDA STATE HORTICULTURAL SOCIETY. 
trash near the trees. Even this will not 
prove sufficient to entirely prevent the dis¬ 
ease from gaining a foothold unless we 
take other factors into consideration also. 
One of the most favorable factors for 
the spread of the disease is moist 
weather, but since this is beyond our con¬ 
trol it will need no further consideration 
except to point out that by allowing the 
trees 'to be plajnted /too /closely and to 
branch too low, an artificial condition of 
extreme moisture may be maintained in 
the grove that is very favorable to the 
spread of the fungus. In such groves 
the disease can be combated only with 
difficulty and cannot be conquered. An¬ 
other factor that we can control to a large 
extent is the condition of health of the 
trees. My observations have shown me 
that anything that tends to weaken the 
tree makes it more susceptible to infec¬ 
tion by this fungus and so reduces the 
power of resistance that when it has once 
gained a foothold it progresses much fur¬ 
ther than is the case with a healthy tree. 
Among the causes of weakness may be 
mentioned excessive moisture, or ex¬ 
cessive drought, starvation or overfeed¬ 
ing with nitrogenous fertilizers so that 
the new growth is soft and flabby. In¬ 
jury from insecticides and even from 
fungicides may favor the entrance of the 
disease, while the presence of scale in¬ 
sects on leaves and twigs, or of lice and 
mites, is also very undesirable. Many 
of you have no doubt noticed the dead 
areas at the margins of the citrus leaves, 
sometimes occupying half or more of the 
leaf surface—marked with concentric 
lines of minute dots. These are mostly 
caused by this fungus and will in a great 
many cases be found to center in a group 
of scale insects that have weakened the 
tissue so that at that spot the fungus was 
able to gain an entrance—a thing that 
it does with difficulty in an uninjured ma¬ 
ture leaf. On the other hand, any treat¬ 
ment that keeps the tree growing vigor¬ 
ously with a firm, hard growth, reduces 
its susceptibility to the disease and en¬ 
ables it, in the majority of cases, to 
check the progress of the fungus before 
very much injury has been accomplished. 
One frequent source of entrance of the 
fungus is through wounds—especially if 
the tree be in a weak condition, so that 
it may often happen when one starts to 
prune withertip out of his grove he finds 
to his dismay in a few weeks that he has 
more of the disease than before, infec¬ 
tion having taken place at every cut sur¬ 
face and having followed down without 
any apparent check from the pruning. 
In a case like this, I would advise that 
a second man follow the pruner right up 
and spray the trees thoroughly with Bor¬ 
deaux mixture within a few hours after 
pruning. In this way the cut surfaces 
will be coated by a layer of Bordeaux 
mixture which will prevent the spores 
of the . fungus from germinating 
and reinfecting the plant. If the disease 
is not abundant in one’s trees and they 
are in vigorous condition, it may not be 
found necessary to spray. 
Recently there have come to my notice 
a number of cases where avocado trees 
have been very seriously injured by this 
disease. Three or four years ago a large 
grove of budded avocados was set out 
in the southern part of the state. The 
owner fertilized it with a great excess 
of phosphoric acid (18 to 25 per cent.) 
while but two or three per cent, of am¬ 
monia and three or four per cent, of 
potash were applied. The trees did not 
make any too vigorous growth and a year 
ago this spring, although not yet old 
t 
