Dark spots are rapidly spreading on leaves of black eyed Susan’s 

Dark spots are spreading on black eyed Susan leaves

These symptoms look consistent to a common fungal disease of Rudbeckia species called Septoria leaf spot. Some Black-eyed susans can have resistance and some varieties or more resistant than others. The Goldstrum variety seems to be the most susceptible but also one of the more commonly planted varieties in Maryland. With our wet spring it is not surprising that this is happening since having wet leaves can cause it to manifest. 

It rarely affects the overall health of the plants but can weaken them some and also take away from their beauty. You can try to remove any infected leaves and also ensure there is good air flow between the plants. As they fade in the fall you can remove any foliage debris to help suppress the overwintering fungal spores. Maybe try to leave up the seed heads for the birds to enjoy though! Yellow finch love the seeds.

The second link we gave does share that it can be controlled with a fungicide spray which we wouldn't recommend in a home setting as it isn't totally fool proof. Fungicides need to be applied preventatively before the infection starts to take effect. They tend to be expensive and need to be applied at regular intervals throughout the growing season. Overuse of fungicides can be harmful to some pollinator insects, as well as disrupting the beneficial soil microbes. 

Let us know if you have further questions, 

Emily