The beautiful bright yellow daisy-like flowers of rudbeckia are often overshadowed by the diseased foliage.
A bacterial and several fungal leaf spot diseases cause purplish-black spots on the leaves of rudbeckia. Severe infestation can totally blacken the leaves and cause the plants to dieback a bit earlier in fall.
Fortunately, most of the diseases are cosmetic and the plants will continue to flower and return each year.
Reduce the risk of this disease by providing adequate light and air circulation around the plants. Use a soaker hose or watering wand to apply water directly to the soil when needed.
In the fall, remove and destroy all diseased plant parts.
If disease is a yearly problem, you can use a copper containing fungicide as a preventative. Or plant something slightly shorter in front of these plants to mask the discolored leaves, but allow the flowers to show through.
Try growing other rudbeckias that are less susceptible to these diseases. The great coneflower (rudbeckia maxima) is native to North America and grows 5 to 6 feet tall. Its large, yellow daisy-like flowers are held high above the 12- to 18-inch long blue green leaves at the base of the plant.
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