On leaves, young infections are very small, greenish-
yellow, translucent spots that are difficult to see. With 
time the lesions enlarge, appearing on the upper leaf 
surface as irregular pale-yellow to greenish-yellow spots 
up to 1/4 inch or more in diameter. On the underside of the 
leaf, the fungus mycelium (the "downy mildew") can be seen 
within the border of the lesion as a delicate, dense, white 
to grayish, cotton-like growth. Infected tissue gradually 
becomes dark brown, irregular, and brittle. Severely 
infected leaves eventually turn brown, wither, curl, and 
drop. The disease attacks older leaves in late summer and 
autumn, producing a mosaic of small, angular, yellow to red-
brown spots on the upper surface. Lesions commonly form 
along veins, and the fungus sporulates in these areas on 
the lower leaf surface during periods of wet weather and 
high humidity.