GRAPE DISEASES 237 
Downy-MILpEw 
Caused by Plasmopara Viticola (B. and C.) Berl. and de Toni 
This disease was first observed in America in 1834. Some 
time prior to 1878 the pathogene was carried to Europe on 
American stock, for in September of that year it was first 
recorded in France. During the five preceding years, French 
growers had been warned against such importations from the 
United States on account of the downy-mildew of grapes. At 
that time European vineyardists were eager to use the American. 
root stock on which to graft French vines as a remedy for the 
grape phylloxera, another pest of American origin which had 
already been so destructive to French viticulture. But in 
spite of the admonitions of the French scientists against im- 
portations from America, the downy-mildew finally reached the 
European vineyards. From France the mildew-pathogene 
spread throughout Europe, where it is now a very troublesome 
foe. In the United States the disease is very generally known, 
being more destructive to European varieties than to domestic 
forms. No variety is notably resistant under all conditions. 
Both smooth and pubescent, wild and cultivated, sorts are 
affected. The downy-mildew also occurs on five-leaved ivy, 
a close relative of the grape. 
The greatest losses to American viticulturists from this 
disease are incurred in northern United States, where in some 
localities it has been estimated that 25 to 75 per cent of the crop 
is destroyed. Losses in Europe have been enormous. The 
disease is destructive not only to the berries but to practically 
all young or green portions of the vine. The nature of the 
losses is as follows: (1) shelling; rotting and mummifica- 
tion of the fruit; (2) spotting of the foliage, often resulting 
in premature defoliation; and (3) sometimes a dwarfing and 
killing of canes and leaves. 
