ISTew York Agkicultukal Experiment Station. 433 



noticed bj a casual observer, is in dry, brick red spots on the 

 upper surface. On the under side of the leaf the diseased area 

 will be covered with the interlaced threads of the fungus. The 

 red spots increase in size until in many instances the entire leaf 

 dies and falls to the ground. It frequently causes the berries to 

 turn dull brown and become soft and shriveled. This appear- 

 ance of it has been commonly called " brown rot." The spores 

 are found on the threads which issue from the under side of the 

 leaves or from the stems or fruit, the whole giving when fresh a 

 glistening white downy appearance from which the disease takes 

 its most common, and preferable name of " downy mildew." Later 

 the parts of the fungus exposed on the surface assume a gray hue 

 and so the disease has also been known as " gray rot." Some 

 varieties, like Delaware, appear to be quite susceptible to the at- 

 tacks of the disease and none of the cultivated varieties are known 

 to be entirely exempt. 



Treatment. — It may be successfully treated in the manner de- 

 scribed for black rot. See page 430. 



POWDERY MILDEW. 



(Uncimda spii-alis B. & C.) 



Description. — Unlike many of our fungous diseases, the pow- 

 dery mildew flourishes best during the dry weather of mid-sum- 

 mer. It usually begins its attack in June, though it may appear 

 earlier. Its name is descriptive of its appearance, as it forms dull 

 white, powdery patches on the young shoots on the upper surface 

 of the leaves. When the fungus is abundant it seriously checks 

 the growth of the vines by absorbing the nourishment that should 

 have gone to their development. The berries may be attacked at 

 any stage of growth and tliey are injured or destroyed in the 

 same way as are the shoots or leaves. 



Trentnirnt.- — It may be successfully treated in the manner de- 

 scribed for black rot. See page 430. 



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