Symptoms first appear as small, angular, yellow lesions on the upper side of the leaf.
A white to purplish mildew may be observed on the lower side of the leaf during humid weather. As the lesions expand, their centers turn brown. Often the margins of diseased leaves curl upward. During favorable weather, leaf lesions coalesce and kill large areas of the leaf surface. This results in a stunting of the plant and a failure of the fruit to mature properly.