This is a photo of young purple blotch lesions. Purple blotch is most often characterized by the purple, bulls-eye lesion seen below. Early symptoms of downy mildew include a purple-grey, velvety growth; however, once infected leaves turn pale-green to yellow and collapse. Another key difference between these two diseases is that while both start out patchy, downy mildew quickly spreads throughout the field and can result in a rapid collapse of plants.