Hello

This looks like septoria leaf spot, very common on Rudbeckia species.

Here is how to manage it:

Septoria leaf spot is caused by the fungus Septoria rudbekiae.

The fungus overwinters in infected plant residue. Spores are produced in late spring and early summer, causing leaf spots on the lower leaves. As the season progresses, lesions develop on upper leaves as well. The spores of the fungus are dispersed by splashing water (either irrigation or rainfall), and can cause lesions throughout the growing season. Like most fungal leaf spot diseases, the spores require moisture to germinate and cause infection.

Management: Remove the infected leaves am mulch around plants at the end of the growing season to reduce the amount of spores available the following year. Mulch with fresh material.

Proper plant spacing will increase air circulation around the foliage and allow leaves to dry off quickly after dew or rainfall events.

Since Rudbeckia plants spread quickly, pull volunteer plants, and thin plants when they are overcrowded.

Avoid overhead irrigation, which will promote leaf wetness and also splash spores from plant to plant. If this isn’t possible, only water in early morning so plants dry quickly in the sunshine, before nightfall.

A general-purpose garden fungicide may help reduce the spread of the disease, but these chemicals are protectants and do not cure infected leaves. Application in early to mid June may help reduce initial infection, and result in a slower onset of disease symptoms. For maximum control, application of a protectant fungicide should be made periodically throughout the growing season (check label for instructions on spray interval and rate). Rotate fungicides so resistance doesn’t build up. Among the compounds registered for use on ornamentals are chlorothalonil, thiophanate methyl, copper compounds, and mancozeb.

Please read and follow all precautions and directions on the label of all garden chemicals.