HYPOPLASTIC DISEASES 
DOWNY MILDEW OF GRAPES 
This is a common disease of both wild and cultivated grapes. It is in 
some years very destructive to certain varieties in American vineyards 
but is far more destructive to cultivated grapes in Europe. It also affects 
the five-leafed ivy, Psedera quinquefolia (L.) Green. 
SYMPTOMS 
This disease affects the leaves, young canes and fruit of the grape. 
On the leaves. Examine the leaves of cultivated grapes provided and 
OBSERVE :— 
1. The location, size, color and general appearance of the spots 
on both surfaces of the leaf. 
2. Difference in the appearance of the old and young lesions, 
especially on the upper surface. The tissues are not directly killed, but 
show a brownish yellow color contrasting sharply with the green of the 
healthy parts. (See autochrome 1.) 
3. The downy white growth covering the under surface of the 
lesion,—the fruit-structures of the pathogene. 
4. The above characters as exhibited by the lesions on the smooth 
leaves of the wild grape. 
Make sKETCHEs of both sides of affected leaves to show the characters 
of the lesions as observed. 
On the canes. The cane-lesions may be either local or systemic. 
Study the specimens showing local invasion. OBSERVE:— 
5. That the lesions are usually on one side of the stem, causing 
it to bend or curl, the diseased area being on the outer side of the curve. 
6. A slight increase in the size of the affected portion of the cane. 
7. The white downy growth of the pathogene, covering the 
lesion in many cases. 
SKETCH to show a localized stem-lesion. 
Examine the specimens (illustration specimens) and photographs of 
systemically invaded shoots. OBSERVE:— 
8. The distinct dwarfing or hypoplasia of the shoot and its organs, 
—the leaves and tendrils. 
9. The continuous white coating of the fruiting structures of 
the fungus. 
SKETCH a portion of a shoot to show these characters. Only very 
young shoots show systemic lesions. 
On the fruits. Examine the specimens and photographs provided. 
OBSERVE :— 
10. That certain of the berries in the bunch are covered with the 
downy white growth observed on leaf and stem-lesions. 
11. That the affected berries are brown in color, in striking 
contrast to the green healthy fruits on the bunch. The disease is, on this 
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