I have had lots of problems with my petunias and geraniums. Seems that around here there is a type of moth that, around the time of the full moon, lays their eggs in those types of plants and then, soon after, the larvae, which I'm told is called a "tobacco bud worm", starts munching away at the blossoms. They have voracious appetites and seem to particularly enjoy petunias and geraniums. Some of the insecticide sprays that I used would wilt the petunias. Finally was directed by a nurseryman to try "Maverick" herbicide. It worked great when I remembered to use it.
Another constant problem here is snails, which will devour a patch of marigolds in nothing flat. LOL.