CHAPTER XXXIV 

 DETAILED ACCOUNT OF SPECIFIC DISEASES OF PLANTS 



This section of the book will be devoted to a consideration of the 

 specific diseases of plants, and the treatment of the subject has been 

 made possible by a selection of nearly loo parasitic and non-parasitic 

 diseases. In this selection, several things have been kept in view, viz., 

 the importance of the disease over wide geographic areas, the system- 

 atic relationship of the fungus in order to connect up the practical and 

 the systematic parts of the book, because our knowledge of the disease 

 warrants its inclusion in the descriptive part which follows. As a con- 

 sideration of the remedial measures used to combat the disease was 

 omitted largely in the description of plant diseases in general, it is intro- 

 duced incidentally with the study of specific plant diseases. The chief 

 reference to such remedial substances and their use will be found in one 

 of the appendices in the back of the book, where the manufacture of 

 sprays and washes and their recommended use may best be made with 

 the consideration of a spray calendar. A regular spraying program 

 is now considered a necessity by every successful plant-grower, the 

 expense of which, treated as insurance, can no more be escaped than the 

 outlay for cultivation, manures, or pruning. In the control of plant 

 enemies, including both insect pests and fungous parasites, there are 

 essential points in practice which may not be evaded or neglected, 

 namely: To spray at the correct time (hence the need of a calendar) to 

 use the proper form and strength of spray (hence the need of formulae) 

 and to make a thorough covering of the parts sprayed. Hence that 

 important branch of phytopathology known as therapeutics will be 

 mentioned incidentally in part III and treated in detail in the latter part 

 of part IV. 



The description of each disease will be given in condensed form pur- 

 posely, so that the student of plant pathology who wants to know more 

 about the specific diseases of some particular crop in which his interest 

 has been aroused will be compelled to study the literature and thus gain 



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