Answer: It's difficult to diagnose a plant problem without benefit of inspecting it first hand, but several possibile causes come to mind:
Rose Midge damage. If your roses seem otherwise healthy but the flowers just don't open properly, its probably caused by the rose midge. These nearly invisible insects scrap new growth particularly flower buds, causing them to shrivel and turn black. Bayer Advanced? Dual Action Rose & Flower Insect Killer Concentrate will control rose midges.
Thrips. Another tiny pest that you'll have trouble seeing with the naked eye, thrips feed on rose petals, causing them to be deformed and discolored. Buds often fail to open properly. Either Bayer Advanced? 2-in-1 Systemic Rose & Flower Care Granules or Bayer Advanced? Dual Action Rose & Flower Insect Killer Concentrate will control thrips.
A third possiblity is that the plant is struggling because of the soil or the way in which it is planted. If you use insecticides against either of the above pests and it doesn't improve the condition, you might want to dig the shrub up this winter and inspect both the planting hole and the root system. There just may be a problem underground....
Best wishes with your roses!
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