Black Eyed Susans
Black-eyed Susans can be susceptible to a leaf spot disease called Septoria. It appears as irregular black spots on the leaves which can cause a disfigurement of the plant with wet, hot and humid weather. Once established, it is difficult to control
Try to improve air circulation, limit standing water, and inspect the leaves regularly. Removing infected leaves, and discard the infected plant material. Do not put in the compost pile.
More information can be found here https://ag.purdue.edu/btny/ppdl/Pages/Rudbeckia-Leaf-Spot.aspx
Hello, There is new information from Howard Russell Entomologist, Plant and Pest Diagnostics, Michigan State University
“Those are Rudbeckia psyllid galls, Bactericera antennata (Hemiptera: Triozidae (Psyllidae in part)).
The insect is reported to have considerable morphological and color variation. The mature nymphs I have observed are about 1/8 inch long, flattened and very colorful with a light green abdomen, red-orange head and thorax, and white wing pads. The eyes are large and the nymph is completely fringed in white hairs. The adult is very small and has two pairs of transparent wings and red eyes. The body is mostly black with brown highlights on the dorsal aspect of the thorax. The legs are two-toned with the bases black and ends tan.
The nymphs feed by inserting their needle-like mouthparts into lower surfaces of the leaf and sucking plant fluids. The nymph’s saliva appears to have systematic effect throughout the leaf. First, a shallow but distinct depression develops at feeding site on lower leaf surface. The tissue surrounding the feeding site turns deep purple on both leaf surfaces. However, the top surface of the feeding site remains green in most cases. The veins may turn purple over much of the lower leaf surface.
For homeowners, the best products for controlling the psyllid are cyfluthrin (sold as Bayer Advanced Vegetable and Garden Spray), bifenthrin (sold as Ortho Bug B Gon) and malathion. Be sure to read and follow all instructions on the label before using any pesticide.”
Hope this gives you an understanding of issues with Black-Eyed Susan.