242 MANUAL OF FRUIT DISEASES 
of short duration followed by sunshine and winds are not 
favorable to the spread of the fungus. Most injury is done 
during hot, wet weather. 
Control. 
Since the fungus hibernates in old fallen leaves it is commonly 
recommended that these be plowed under early in the spring. 
The real value of such an operation, however, is not definitely 
known. The vines should be sprayed to protect them against 
attacks of the downy-mildew pathogene in any case. Use 
bordeaux mixture 5-5-50, making five or six applications 
during the season. The first should be made just before the 
blossom buds open; the others at intervals of two weeks. 
REFERENCES 
Istvanfi, G. Etudes sur le rot livide de la vigne. Hongrois Royal 
Inst. Cent. Ampel. Ann. 4: 1-260. 1913. 
Viala, P. Les maladies de la vigne, pp. 57-185. 1893. 
Farlow, W. G. On the American grape-vine mildew. Bussey Inst. 
Bul. 1: 415-425. 1876. 
Gregory, C. T. Spore germination and infection with Plasmopara 
viticola. Phytopath. 2: 235-249. 1912. 
Shear, C. L. Insect and fungous enemies of the grape east of the 
Rocky Mountains. U.S. Agr. Dept. Farmers’ Bul. 284 : 30-32. 
1907. 
Gregory, C. T. Studies on Plasmopara viticola (Downy mildew of 
‘grapes). Int. Cong. Vit. Rept. 1915: 126-150. 1915. 
Powpery-MILDEW 
Caused by Uncinula necator (Schw.) Burr. 
The powdery-mildew, or oidium, of the vine is native to the 
Old World, originating on native plants in Japan. It was at 
one time erroneously held that this disease, like black-rot and 
downy-mildew, originated on wild vines of the eastern and 
central United States. The disease first appeared in Europe 
