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 (epiphytotios) 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. 



