Spraying for Citrus Diseases 
ITS USEFULNESS AND ITS LIMITATIONS 
Prof. R. R. Fulton 
Spraying has come to have an estab¬ 
lished place in combating many fungous 
diseases of various forms, garden and or¬ 
chard crops. It is used most generally on 
crops that have a relatively high value per 
plant, and against diseases that attack the 
crops at such times and in such ways as to 
render the use of spray materials feasible. 
We are concerned at this time with citrus 
fruit crops, valuable enough to justify 
considerable expenditures to insure fruit 
free from fungous blemishes, to protect it 
from the more destructive fungous rots, 
or to maintain the health of the trees in 
all their parts. Spraying, it must be re¬ 
membered, is not a cure-all to give relief 
from all the ills our trees are heir to. It 
is only one of a number of means for 
combating diseases, useful in its particu¬ 
lar and somewhat limited sphere, and 
usually most effective when used in con¬ 
junction with other defense measures. 
It is my purpose tonight to review 
some of the fundamental principles on 
which the practice of spraying for fun¬ 
gous diseases is established, and to discuss 
the relations of these to the citrus crop. 
I do not enter upon any discussion of the 
other broad field for spraying, the control 
of insect pests. If I speak in rather gen¬ 
eral terms, you will bear with me, remem¬ 
bering that spraying for the diseases of 
citrus fruits is still in the experimental 
stages. For various reasons its develop¬ 
ment has lagged behind spraying for cit¬ 
rus insect pests. You will remember, 
too, that your speaker is now in the midst 
of his second season’s work on the rather 
complex problems involved, and is not yet 
ready to make an extended report on the 
results of the experiments. 
The diseases we deal with are caused 
by fungi, and fungi are themselves mi¬ 
croscopic plants of a low order. Many 
are parasites attacking some living plant 
as a host, and, as a rule, these attack most 
vigorously particular varieties or species 
and affect other kinds of hosts less vig¬ 
orously or not at all. Furthermore, the 
attack is usually restricted to one or more 
particular organs of the host, and to some 
special condition of such susceptible parts, 
such as age, vigor of growth, succulence, 
etc. 
Before the parasite develops in the host 
plant tissues, the reproductive body of the 
fungus must come in contact with it, after 
being transferred from some other place 
in which it was previously produced by 
fungus growth of like kind. This law is 
as absolute and no less mysterious than 
that every plant of higher order, corn, 
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