Sick rose

Looks like balling and browning from rain to me, although I can see some black objects on the bud next to the opened flower - I can't tell what they are though. If the rose is otherwise healthy in the leaves, as you say, then that's all it is. Remove the flower.

I have a lovely pink rose that does exactly the same thing when it's been raining. I just snip away the disfigured bloom and wait for the new buds to open in the sunshine. If the rain has been particularly heavy the buds will ball and brown without ever opening, but it does no harm to the bush. I just snip those away too.

Does this happen with other plants, too, such as Dianthus? Sometimes the flowers on my Dianthus seem to rot, and other times they rot before the buds even open. So is it likely to be rain?

Could be, I guess, though it might also be some kind of mildew affecting the plant. Rain definitely affects Pelargonium geraniums - the flower heads look awful after a lot of rain. And even worse is if the sun comes out and its hot after rain.

Sometimes the damaged petals harden and become paper-like, then the flower can't open. Best to cut them off and wait for new buds to form.

Thanks folks for your helpful and reassuring replies. The damaged roses have duly been snipped. Bamboo, the objects you spotted on the bud turned out on closer inspection to be greenfly, so they also are gone!!