Several leaf spots diseases can cause the symptoms you described. You like many gardeners are finding the once low maintenance Black-eyed-Susan (Rudbeckia) to be a disease ridden plant. The first step in controlling this disease is fall cleanup. Make sure to remove and destroy disease infested foliage. Thin plantings in spring for improved air circulation and avoid overhead watering that can spread disease. Several fungal leaf spot diseases cause irregular black spots on the leaves and stems of Rudbeckia. If cultural controls (sanitation, thinning and proper watering) don’t stop the problem you may decide to use chlorothalonil or a copper fungicide. Apply in spring before the symptoms appear. Angular leaf spot, caused by a bacteria, looks very similar. The same cultural recommendations apply to this disease. Applications of a copper based bactericide like Bordeaux will help reduce the risk of this disease. Make the first application in spring and repeat as advised on the label. See the University of Minnesota Extension fact sheet at www.extension.umn.edu... for pictures and more details on these and other problems with Rudbeckia.