Vegetable and Field Crops 



179 



characteristic white hyphse and spores tinged with purple 

 may be seen on the under sides of the older spots. The 

 disease progresses to the younger leaves, slowly in dry or 

 cool weather, but very rapidly in warm, wet weather. The 

 field is soon reduced to a mass of dry, dead leaves. 



Fig. 97. — Spots of downy-mildew upon cucumber leaf. After Orton. 



The mildew was first described in 1868 from Cuba. In 

 1889 it attracted attention in the United States (New Jersey, 

 Florida, and Texas) and in Japan. Since that time it has 

 been destructive in many states. The loss in Wayne County, 

 Ohio, alone was estimated at $45,000 in one season. 



It grows upon muskmelons and cucumbers in most de- 

 structive form and is less injurious to squash, pumpkin, 



