SPRAYING. 



H. H. WHETZEL, PROFESSOR OF PLANT PATHOLOGY, 

 CORNELL UNIVERSITY, ITHACA, NEW YORK. 



There are four fundamental principles upon which all methods 

 for controlling plant diseases are based, namely, exclusion, 

 eradication, protection and immunization. 



It is upon the first of these, exclusion, that all quarantine 

 and similar exclusionary methods and measures are based. 

 The United States quarantine act of 1912, together wuth its 

 numerous amendments, the rules based thereon and quaran- 

 tines laid thereunder by the Federal Horticultural Board 

 constitute the most extensive application of this principle ever 

 undertaken. Upon the soundness of exclusion as a fundamental 

 principle in disease control there can be no question; upon 

 the practicability or advisability of its application for the 

 exclusion of foreign pathogenes and pests from this country 

 under modern conditions of commerce and transportation, 

 there is abundant ground for honest difference of opinion 

 which only trials and time can settle. 



Eradication of pests and pathogenes which have become 

 established in crop areas of larger or smaller extent has been 

 applied in this country during the last decade on an extensive 

 scale in a number of notable cases, as, for example, the chestnut 

 blight, the white pine blister rust, the citrus canker, and several 

 insect pests. Remarkable success is claimed in a number of 

 these cases, while in others equally notable failure is admitted. 

 The eradication of certain disease-inducing fungi, such as grain 

 smut, the potato scab organism, etc., from limited areas has 

 long been regarded a successful practice. 



