CHAPTER XXIII 



Some Common Diseases of Plants 

 and Their Control 



By Edwin F. Hopkins, Associate Pathologist, Alabama Agri. Exp' 



Station, Auburn, Ala. 

 and 



H. H. Whetzel, Professor of Plant Pathology, Cornell University, 



Ithaca, N. Y. 



How Diseases in Plants are Exhibited — The Cause of Disease — 

 Concerning the Control of Diseases — Materials Used to Control 

 Plant Diseases — The More Common Diseases of Garden Crops 



INCREASING attention is being given these days to the diseases 

 of plants because of the enormous losses which they annually 

 entail. Jn addition to the fact that some of these diseases take 

 a certain yearly toll from our crops and thus reduce production per 

 acre, there is the danger that under favorable conditions certain dis- 

 eases of staple crops may become epidemic and totally wipe out a 

 product, vitally necessary to our welfare. The late bUght of Potatoes 

 it is said, contributed chiefly to the suffering caused by the Irish 

 famine in 1845. That year, being a favorable one for the blight, the 

 potato crop throughout Europe was a total failure. Taking some more 

 recent, more local, figures, in New York State alone, it is conservatively 

 estimated that Oat smut caused a loss of over $2,000,000 in 1915, 

 while the same state that year suffered a loss of nearly 20 millions of 

 dollars from the late blight of Potatoes. Wheat rust is credited with 

 having caused a loss of $67,000,000; in 1898, Peach leaf curl damaged the 

 1900 Peach crop in the United States to the extent of $2,335,000. 

 And while figures are not available, losses from plant diseases in home 

 gardens are without doubt equally appalhng in the United States. 



One could give many more figures, but these few will serve to 

 illustrate the importance of understanding and controlhng plant dis- 

 eases. We must realize that they are present, that they cause an 

 enormous loss and that every grower and gardener must learn three 

 things regarding the more common of them. These are, first, just 

 how to know them; second, what causes them; and, third, the method 

 of control. 



How Diseases in Plants are Exhibited ^ 



The presence of a disease is made evident by certain signs or 

 symptoms shown by the diseased plant. These are injurious deviations 



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