We can safely say that it's one of two diseases that are common to Rudbeckia, bacterial (angular) leaf spot or Septoria leaf spot, a fungal disease.

The affected plant should be removed, pronto. Avoid overcrowding and overhead irrigation. These diseases can spread rapidly through an area that is watered by a sprinkler system. All fallen leaves need to be removed.

In the fall, the planting area should be meticulously cleaned up, even removing the mulch.

There are fungicides that are effective for Septoria as well as copper sprays that can be useful for the bacterial leaf spot as well as the fungal disorder. But the most important aspects of gaining control is removal and housekeeping.

Thank you. It affected only two plants and I removed them right away. No sprinklers there. Maybe a little crowded. Will keep an eye on my other plants. That was the only rudbeckia that was blooming!!
Anyway appreciate quick answer and advice.