DISEASES OF GRAPES 



DR. DONALD REDDICK 

 Professor of Plant Pathology, Cornell University, Ithaca, N. Y. 



The early attempts at grape culture in 

 the United States without exception were 

 failures. It is now known that these failures 

 were not due to uncongenial soil, as was 

 believed at^the time, but to the ravages of 

 diseases which are much more destructive 

 to European sorts than to those indigenous 

 to America. The black rot disease, the 

 downy mildew, and the powdery mildew are 

 the diseases chiefly concerned. When these 



troubles were finally introduced into Europe they proved as 

 destructive as they had previously been in European sorts grown 

 in America, and it was only the very fortunate discovery of 

 bordeaux mixture and its effectiveness against downy mildew 

 that saved European viticulture from extinction. 



Following the early failures with European varieties began 

 the amelioration of American grapes, all of which are more re- 

 sistant to the indigenous American diseases than are the European 

 varieties. This difference in susceptibility is exhibited in hy- 

 brids between the two, and varieties having only one-eighth 

 European " blood " almost invariably exhibit a marked sus- 

 ceptibility to those diseases. It should be remembered at the 

 outset, then, that the pedigree of a variety will furnish an im- 

 portant indication of its probable susceptibility to disease. 



BLACK EOT 



This disease is very common in the Central Lakes region and in 

 the Hudson district, but it rarely appears in the Chautauqua belt 

 and, when it does, is not very destructive. The disease is caused 

 by a fungous parasite, Guignardia bidwellii, which passes the 

 winter in the hard black mummies on the dead tendrils, or on 

 small dead areas on the canes. The disease first appears in the 

 spring in the form of brown leaf spots about one-fourth inch in 



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