Answer: Based on your description I think your plant is suffering from powdery mildew. This seems like a white powder covers the plant and occurs under certain weather conditions and in locations where air circulation is poor. Remove the worst affected foliage. Try rinsing it off with water from the garden hose. Then you could try treating with a fungicide containing sulphur. Be sure to read and carefully follow all of the label directions. Move to a location with good air circulation and avoid overhead watering.
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