PREFACE 
IT is the common opinion of authorities that fruit-growers 
lose millions of dollars annually on account of diseases of 
their crops. It has been estimated that 75 per cent of this 
loss may be prevented by spraying — the chief method 
of fruit-disease control. 
In order to understand and to perform properly the meas- 
ures of fruit-disease control, it is essential that some knowl- 
edge of the cause of the disease in hand be acquired. In 
recent years scientists and laymen alike have recognized the 
importance of certain technical details regarding the cause 
in order to undertake the prevention of these losses. Simi- 
larly, the value of other facts must be apprehended, such as 
the history of a disease, where it originated, with what 
rapidity the pathogene has spread, ‘the losses it is capable of 
incurring, and under what conditions these destructive out- 
breaks (epiphytotics) occur. 
As evidence that the practicing agriculturists are rapidly 
becoming acquainted with the value of scientific knowledge 
regarding diseases of plants, it is only necessary to point to 
their interest and cooperation in the matter of obtaining 
accurate information under field conditions. The prejudiced 
and critical attitude of the grower is now for the most part 
of no consequence. Little self-protection is now needed by 
the experimental plant pathologist; the grower’s attitude is 
no longer antagonistic, but he is friendly and, what is more 
encouraging, he seeks with confidence the advice of the 
phytopathologist. 
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