6 UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



disease itself was not described. The reader was left to conjecture, 

 from the name the grape-growers were agreed upon giving to it, that a 

 red leaf was its main characteristic. Beyond this, however, the grape- 

 growers did not entirely agree ; the term red leaf is indefinite enough 

 to allow of a wide individualistic interpretation, and the grower who 

 had vines suffering, or dying, from a cause undiscoverable to him, and 

 showing a foliage tinted, perchance, here and there with red, was 

 inclined to call the trouble from which his vines were suffering the 

 Red-leaf disease. This diversity of opinion was at first rather confusing, 

 and was more a hindrance than a help in furthering the investigations. 

 In fact, of the three vineyards kept constantly under observation, only 

 one was finally found to be free from any other disease than the Red- 

 leaf ; and the development and characteristics of the said disease in 

 this vineyard were a great help in diagnosing the malady in other 

 parts of the county, and under less favorable circumstances. 



The result of our investigations of the disease under consideration 

 may be conveniently divided into two parts : (1) Description of the 

 Red-leaf disease and its relationships ; and (2) Results of the winter and 

 summer spraying experiments instituted to combat it. 



DESCRIPTION OF THE DISEASE AND ITS RELATIONSHIPS. 



The Red-leaf disease may affect the shoots, the leaves, the peduncles, 

 the pedicel, and the fruit of the vine; it may affect the uppermost part 

 of a cane, or several canes; one entire side of a vine, or, but more 

 rarely, an entire vine. One vine may show all the characteristics of 

 this disease, and another only a part, or perhaps,, only one of them- 

 The disease may never proceed beyond the first stages, a not uncommon 

 feature, or it may develop sloAvly until all its characters are patent to 

 the most casual observer; more often, however, its development is rapid, 

 and it would be somewhat difficult to distinguish the first stage, which is 

 rather obscure, from those final stages which characterize it particularly. 



Allowing, then, for the irregularities in the development of the Red- 

 leaf disease, and for the absence of anything like progression from one 

 stage to another, the reader will find in the following description the 

 means of identifying this disease, without much difficulty, whenever it 

 occurs in his vineyard. 



Effect of the Disease on the Leaves. The leaves near the apex of the 

 shoots, including those recently expanded, and perhaps for a foot or two 

 down, become pale, especially in the interveinar spaces. If a leaf in this 

 stage is picked and observed by transmitted light, and with the under- 

 side facing the eye, all the fine network of veins will be found to be 

 discolored. This discoloration of the small veins appears simultane- 

 ously with the loss of color in the leaves; in the recently expanded 



