Q: I’m seeing petunias with white spots on the flower petals. There are no spots on the foliage.
A: It’s probably gray mold, Botrytis cinerea, a common disease of flower petals. If a petunia flower is kept constantly moist, the mold will turn the bloom into a gunky mess. But in typical summer weather, heat dries the fungus before it can go further than the initial infection. You can prevent it by spraying with chlorothalonil (Daconil) at planting.