I have Black Eyed Susans through the gardens surrounding our house. Most show...
I have Black Eyed Susans through the gardens surrounding our house. Most show the problems seen in the photos: leaves covered by brown spots and flowers that are not fully formed. Although the flowers appear to have been eaten , I have never noticed insects on these plants. This has been a problem for a couple of years and I pulled up one section of older plants, but am now seeing the problem in other sections. I don't use pesticides in my garden. Is there any hope or should I dig up and get rid of all infected plants?
Black-eyed Susan can be susceptible to a leaf spot disease 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. 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. A general purpose garden fungicide may also help reduce the spread of the disease, but these chemicals are protectants and do not cure infected leaves (check label for instructions on spray). 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.