So far as we can tell, both photos show spent blooms, rather than flower buds that have been damaged by disease or pests.
The petunia flower shown appears to be healthy. The adjacent sepals surround a brown, cone-like structure that is a ripening seed capsule. (The flowers that preceded the capsules dried up and fell off a while ago.)
Here is a spent dahlia flower that resembles the one shown in your photo. These can simply be removed to improve the plant's appearance.
If there are still damaged flower buds that we should see, please reply to this message and attach photos.