VEGETABLE AXD FIELD CROPS 231 



the white spots of the downy mildew which may occur in 

 association with this disease. The damage may be very 

 great, in many instances resulting in the death of the plants 

 or complete loss of their usefulness. 



CUCUMBER 



Downy mildew {Pseudoperonospora cubensis B. & C.) Ros- 

 ten. — This downy mildew first shows its presence by yel- 

 lowish angular spots 3-6 mm. in diameter upon the leaves as 

 seen from above. These appear first upon the older leaves at 

 the center of the plant. The spots become more distinct, 

 enlarge, increase in number, and soon the whole leaf be- 

 comes pale, sickly, and dies. If the weather is moist, the 

 characteristic white hyphse and spores tinged with purple 

 may be seen on the undersides 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. 



The mildew was first described in 1868 from Cuba. In 

 1889 it suddenly 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 cantaloupes and cucumbers in most de- 

 structive form and is injurious to squashes, pumpkins, 

 watermelon, gourds, and other cucurbs. The fungus 

 winters out of doors in the South and in the greenhouse 

 in the North and spreads thence to the fields annually if 

 weather conditions are favorable. 



This disease is often injurious to cucumbers under glass 



