Answer: Rose of Sharon is a very sturdy plant so I would not expect to see that response to the drought (my own plants are fine and they were not watered at all last year) in an established plant that had been in place more than three years. Instead, given the damp season this year, you mightbe seeing the signs of fungal or bacterial infection.
Another possibility is that the plant is being strangled by its own roots; this can happen if encircling roots are not dealt with at planting time and are allowed to continue to grow in a circular pattern. They then fail to extend into the native soil and eventually some years later the plant will indicate the problem by seemingly suddenly failing to thrive.
You might want to consult with your county extension (696-3500) for a more specific diagnosis and if it is a fungal/disease problem, the best treatment for it (if any is needed).
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