GRAPE DISEASES 237 



DoWNY-MlLDEW 

 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. 



