48 Farmers’ Bulletin 1220. 
mercial grape culture have disturbed the equilibrium which had 
become established between the vine and its parasites in their wild 
state, and have facilitated the reproduction and distribution of the 
diseases. In the selection and breeding of the grape attention has 
been devoted chiefly to the improvement of the fruit, and this has ap- 
parently resulted in some cases in a decrease of the natural powers of 
resistance to disease originally 
possessed by the wild vines. 
In certain sections of the 
country where grape growing 
was once a profitable industry 
it has largely been abandoned, 
chiefly on account of the great 
loss caused by disease. The 
amount of loss from fungous 
diseases of the grape in the 
United States varies greatly 
from season to season, accord- 
ing to conditions, varieties, and 
treatment. In the past they 
have frequently, in certain lo- 
calities, caused a total loss of 
the crop when no preventive 
measures have been taken. The 
principal cause of the failure 
of the early American fruit 
growers in their attempts to 
grow the European varieties 
of grapes seems to have been 
the severe and destructive at- 
tacks of our native fungous 
diseases to which the vinifera 
Itc. 538.—Colon of grape phylloxera and its Pris 
distortions on vinifera grape root. Con- 2Yrapes were more susceptible 
siderably enlarged. than the native varieties. 
Injury due to fungous parasites depends largely upon weather 
conditions. The conditions most favorable for the development of 
the majority of the fungous diseases are excessive moisture and heat. 
The general physiological condition of the vines is also important. 
Vines which are kept thrifty and vigorous by proper care and culti- 
vation are not likely to suffer as severely from most diseases as those 
which are neglected. Different varieties also show different degrees 
of susceptibility to the different diseases. 
The principal fungous diseases in the order of their importance 
are black-rot, downy mildew, powdery mildew, anthracnose, ripe-rot, 
dead arm, and crown gall. There are also some minor diseases, but 
