Answer: I think the reason for the change in color is that your lavender rose was grafted onto a vigorous root stock. Over the years the rootstock sent up new canes which were not pruned off. Because they are so vigorous, they overtook the grafted rose. This can also happen if the graft union (swelling on the main stem) is damaged and the grafted rose dies, leaving plenty of growth room for the root stock to send up new canes. You may be able to prune off the canes that are producing red flowers if you follow the cane down to its point of origin. If it is coming from below the graft, you can cut it off. If you cannot find a graft, it may have died over the years and your only recourse is to replace the plant.
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