Answer: It sounds like you had a grafted rose, meaning a top taken from one type of (desirable) rose and grown on the roots of another (vigorous but less desirable) rose. When something happens to the top so that it is weakened or killed back, the root stock may send up shoots of its own. This will begin to overwhelm the original top and/or replace it. When this happens, there are two possibilities. One is that you can prune away the canes originating from the root stock and thus force the plant to send its energy to the remaining desirable canes. The other is that there are no canes left from the original top, in which case there is nothing you can do except replace the whole thing. You'll have to take a careful look and see if any of the original top is left.
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