Answer: There is a tiny little winged insect called a rose midge that can cause damage to the petals of unopened rose buds. These very small insects lay their eggs at the base of a rose bud and when the eggs hatch, they feed on the buds which causes them to be damaged or just blacken and not open. A rose midge is a bright green bug and if you take a piece of paper and tap the end of the rose on it, if they are still there, you will be able to see them. Any insecticide will get rid of them just follow the directions on the package.
Another reason might be that when the weather is very hot and the rose bush doesn't get enough water. Red roses and multi colored roses are prone to burning in hot sun so perhaps that's what's happening to yours. A final consideration is a fungal disease. I'm afraid you'll have to put on your detective cap and explore all of these possibilities to determine just what might be affecting your roses.
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