Why would Black Eyed Susans get dying grayish dry leaves?
The condition you describe is powdery mildew, an unsightly but harmless fungal infection that is common in hot, humid weather. The spores of the fungus live in the soil and are splashed onto the leaves of the affected plants when watering. Mondarda, phlox and Shasta daisies are also susceptible. To lessen the severity of the mildew, make sure there is good air circulation around the rudbeckia. That is easier said than done in a typical Chicago summer, so we just learn to live with it!
