244 MANUAL OF FRUIT DISEASES 



better than the fungi concerned in the other diseases mentioned. 

 If not controlled, the oidium does considerable damage in 

 western vineyards. In the Chautauqua region of New York 

 growers may in cases of severe infestation lose fifty per cent of 

 their grapes on account of shelling due to the powdery-mildew 

 fungus. The Lindley is very susceptible to the disease. 



Symptoms. 



All green parts of the vine may be affected : leaves, canes, 

 flowers and fruit. The young leaves at first show whitish or 

 greenish white patches on the upper or lower surfaces. A 

 mottled appearance is thus produced. These patches later 

 run together until a large portion of the leaf is covered with a 

 grayish white mildew. Sometimes this dense growth of the 

 pathogene is accompanied by malformation and discoloration 

 of the affected leaf. A vine with diseased foliage has a wilted 

 and dwarfed aspect; this is particularly true in the earlier 

 parts of the season and in warm, dry weather. An affected 

 vine emits a moldy odor. Eventually black, pimple-like fruit- 

 bodies of the fungus are seen scattered over the mildewed area. 



Often the mildew is abundant on the shoots. It appears 

 near the base of the canes and at first is not noticeable ; later 

 the affected portion acquires a grayish tint and it is then more 

 easily seen. In severe cases whole canes are covered ; in mild 

 attacks the mildew is confined to patches. Later affected canes 

 turn dark, owing to the injury to the outer bark-cells. If young 

 canes are affected, they fail to mature properly and often they 

 become blackened over their whole surface ; this appearance is 

 sometimes mistaken for anthracnose. 



Sometimes the mildew appears on the flowers, if conditions 

 are favorable in the vineyard during blossoming. This occurs 

 regularly in France, but does not occur in eastern United States. 

 Affected blossoms fail to set or develop in an aborted fashion. 



Diseased young berries are dwarfed and are caused to drop. 

 If not affected until older, the fruit continues to develop, but 



