Black leaves on Brown eye susans

Asked July 16, 2013, 10:23 AM EDT

I have several brown eyed susans in amoungst daisys and pink cone flowers and other plants. One of the BES leaves has many totally black leaves so I placed a large plastic bag over it and dug it out. I also noticed that some of the other near-by BES have a few black spots on the leaves. Should I dig them out also or is there something that will stop the spread? Thank you for your help.

Lackawanna County Pennsylvania

1 Response

Without seeing the leaves, one can only guess what may be infecting your brown eyed susans. You could take a sample if the infected leaves (in a closed baggie) to the local extension office to be sent to Penn State for analysis. Many of these diseases con only be identified by using a microscope. Listed below is a description of one of the most common leaf problems of brown eyed susans.
The fungus Septoria rudbeckiae is one of the most common foliar pathogens of Rudbeckia.
Symptoms begin as small, dark brown lesions that enlarge from 1/8 to 1/4 inch in diameter. Although the lesions are usually rounded, there may be angles where leaf veins limit the spread of the fungus (Fig. 2). Symptoms of this disease may be difficult to distinguish from those of angular leaf spot of Rudbeckia.
Microscopic examination of the lesion will reveal black, flask-shaped structures called pycnidia that contain thousands of thread-like spores. Spores are produced in late spring and early summer, causing leaf spots on the lower leaves. The spores of the fungus are dispersed by splashing water, with lesions first appearing on lower leaves and later developing on upper leaves as the season progresses.
To manage this disease, remove the infected leaves at the end of the growing season to reduce inoculum levels. Because leaf moisture is essential for infection to occur, increase air circulation around the foliage by properly spacing plants (and removing volunteer seedlings) to prevent over-crowding. As with other foliar disease problems, avoid overhead watering. Fungicides containing chlorothalonil or copper* may protect new growth and reduce the spread of the disease. Preventative applications of fungicides should begin in early to mid June prior to the onset of symptoms.