54 THE GRAPE. 



DOWNY MILDEW (Poronospora viticola). This fungus may at- 

 tack the young wood, flowers or fruit, or all these at the same time. 

 When it attacks the foliage it first appears as greenish-yellow or 

 brownish irregular spots on the upper surface, with corresponding 

 spots of whitish frost-like mildew on the under side. The effect of 

 this is to cause the leaves to dry up and fall off, frequently when 

 the fruit is quite green, which consequently does not ripen. 

 But besides the loss of the fruit from this disease the wood is often 

 left in a very immature state, and the whole plant so seriously 

 weakened that it will not produce a full crop of fruit for several 

 years. It frequently acts in this manner on the Delaware, while it 

 seldom injures the fruit of that variety. On other varieties the 

 fruit is more susceptible than the foliage, and it produces brown 

 rot of the berries, which may cause severe losses some seasons. In 

 this case the first perceptible effect of the disease is when a pur- 



FIG. 40. FIG. 41. 



Berries affected with brown rot. Berries affected with black rot. 



plish spot appears on the side of the berry. .Later, the fruit is 

 covered with a white mould, and in a short time the whole fruit 

 turns brown, and later on becomes soft and wrinkled. Figure 40 

 shows a cluster of mouldy berries. 



BLACK ROT affects the fruit which it seldom attacks until the 

 berries are two-thirds grown; these shortly dry up, turn black, 

 and remain hard and dry on the vines, often until the following 

 spring. Each dried berry is covered with minute postules. This 

 disease is only occasionally injurious in the northwestern states. 



Preventives. There are no remedies for either of these dis- 

 eases, for after the fungus finds a lodgment in the tissues of the 

 plant we are powerless to destroy it without injuring the plant 

 itself. Consequently every effort should be used to keep the fun- 

 gus from getting a hold on the plant. It has been found that where 

 the vines are closely shut in, so that there is but little circulation 

 of air and the water does not quickly dry off the foliage, or where 



