120 



Diseases of Economic Plants 



r^ 



^73 



GRAPE 



The high acreage value of the crop, the long life of the 

 individual vine, the numerous, serious diseases to which the 

 vine is subject, and the fact that it was one 

 of the crops first to be commercially sprayed, 

 renders the grape of especial interest to the 

 plant pathologist. 

 ■Black-rot ^^^~^^^ (Guignardia hidwellii 



O^ (Ell.) V. & R., Phyllosticta). — This wide- 

 g spread and exceedingly destructive disease, 

 ■:= the first record of which dates back to 1861, 

 I ^- has been responsible for the abandonment 

 of grape culture in many sections of the 

 country. It is of general distribution 



» y 5 -a throughout the United States, also in 



\^^^^^^ "Z i Europe and Asia. In 1906 in Michigan the 

 loss from black-rot was estimated at 30 to 

 40 per cent of the crop; in Ohio in 1905 at 

 30 per cent of the crop worth $95,000. In 

 many sections the loss is practically total 

 unless measures are taken to check its 

 ravages. 



In its most familiar form the disease con- 

 sists of spotting and decay of the fruit. 

 Black or brown spots, one or more in num- 

 ber, at first infinitesimal in size, appear 

 upon the berry. The spots enlarge with 

 great rapidity, one spot in a few days en- 

 compassing the whole berry and changing 

 it into a black mass. As the rot progresses 



J^^^^^i d the skin remains intact, and soon the berry 



*^i^BPI's&,1 ^ begins to shrink and shrivel until it is 

 eventually merely a dry, hard, wrinkled, 

 mummified fruit. The rapidity with which 



this change takes place is shown in the accompanying figure. 



Many of the berries so mummified fall to the ground, others 



remain upon the vine. 



