New York AGRICULTURAL EXPERIMENT STATION. 433 
noticed by 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. 
(Uncinula spiralis 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 they are injured or destroyed in the 
same way as are the shoots or leaves. 
-Treatment.— It may be successfully treated in the manner de- 
scribed for black rot. See page 430. 
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