I work with the flowers at Eagle Creek Golf Club in Willmar, MN. We have LOTS...
I work with the flowers at Eagle Creek Golf Club in Willmar, MN. We have LOTS of rudbeckia plants. For the past two or more years the leaves on these plants have gotten black - sometime we have had to cut them back early as the leaves looked so bad. What should we do? Is there something we could put in the soil? I have tried a spray suggested by a nursery but since they are on the course they get lots of watering and I am thinking that perhaps this gets washed off before it can do any good as it doesn't seem to help. Thanks!
Kandiyohi County Minnesota rudbeckia
It sounds like these Rudbeckia have Septoria leaf spot. This is a common ailment and is made worse by wet, cool weather. If these plants are receiving a lot of water from the sprinkler system on the golf course it may be hard for you to achieve good control of the disease.
Here is a link that describes this fungal disease, and some of the ways you can try to treat the plants:
I hope this is helpful. Please contact AaE again if you have further questions.