Preventing Leaf Spots
August 8, 2014
How to Prevent Rudbeckia Leaf Spots
By Beth Reid, Perennial Manager
So what causes those ugly purplish-brown leaf spots on your Rudbeckia (Black-eyed Susans) and Echinacea (Coneflower)? Two fungi called Septoria and Cerospera. The infection usually starts on the lower leaves early in the season long before it becomes noticeable on the outer leaves. Warm temperatures and moisture on leaves for extended periods of time favor development of these organisms. High humidity and temperatures during August accelerate the leaf blight which is why it becomes obvious to you, the gardener.
While these infections don’t usually cause plants to die, they can become eye sores. In order to prevent or lessen the spread of the fungi, avoid wetting the leaves in the afternoon. When you do water, do it early in the day so the foliage can dry throughout the day. Preventative sprays of Daconil (chlorothalonil) or a copper-based fungicide applied early in the season can also help. Be sure to clean up dead and infected leaves as the spores overwinter in infected leaves. You may also consider replacing your Rudbeckia or Echinacea with resistant perennials such as Sedum, Coreopsis, or Daylilies.
Feel free to email Beth your plant questions at firstname.lastname@example.org.