Rubekia Brown Spots
You can send us photos so we can see what you are dealing with.
Rudbeckia can be susceptible to several leaf spots. The most common one is called septoria. The disease shows up as irregular black spots on the leaves. This can disfigure the plant significantly if the weather is favorable, wet, hot and humid. Once established, it is difficult to control.
Try managing the bed culturally. Alleviate poor air circulation, crowded conditions, or standing water to help lessen humidity levels. Keep mulch thin and away from the base of the plants. Inspect new foliage and older foliage regularly for signs of infection to catch infections early. Removing infected leaves if there are only a few helps.
At the end of the season really clean up the area well, discard the infected plant material, don’t put in your compost pile. Monitor throughout the season and if disease pressure is heavy, you may want to consider growing something else.