This looks like a fungal problem on your Rudbeckia. There are several fungi that can cause the leaves to be spotted or all brown, and without culturing in a lab it’s impossible to know which one you have, but the cause and treatment are the same. 1. The most common cause of leaf fungi on Rudbeckia is the splashing of water on the leaves. This might be from frequent hand watering, automatic irrigation, frequent rainfalls, or a combination of all of these. Be sure that Rudbeckia, a drought-tolerant plant, is only watered every 7 days. 2. Once your plants have had this problem you’ll want to use one of the organic fungicides next year to help protect the foliage once the watering has been altered. Your local garden center can suggest a product but you might try sulfur, copper, Actinovate or Serenade used according to directions. Start spraying early in the summer and apply every week to ten days to prevent the foliage from being infected.
3. Be sure your Rudbeckia is watered in the AM only, not at night when it will stay wet for longer. Be sure to grow this plant in full sun – in part-shade it is more likely to stay damp and develop fungal conditions.
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