Answer: It is fairly common for Rose of Sharon flower buds to fall off or turn brown before they can open. Usually, the culprit is too much water or uneven watering. Or, it can be caused by insects. Thrips or some other some insect gets into the flower buds and cause the damage. They are difficult to control because they are inside the flower buds. You might attempt to spray with an insecticide but normally the problem tends to run its course and then flowering returns to normal. If you've already used an insecticide, it should have some residual effect and the black bugs should be controlled in time.
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