What is wrong with my petunias?
It is probably due to the flower being wet from watering, rainfall or heavy dew and then not drying off. Try not to spray water on the blooms when you water and try to provide good air circulation. Water in the morning so they have all day to dry off rather than in the evening so that they stay wet all night. Remove the blooms and if you are fertilizing regularly you will have replacements in no time. Petunias need fertilizing regularly in order to produce lots of blooms all summer.