I live in South Florida and have planted New Guinea Impatiens near some hedges and around a tree. I fed them with osmocote and have been watering them every other day. I water them fairly early in the morning, before the sun comes up. Lately, I have noticed that some of the leaves are bleaching, i.e., there are some white spots developing. I should add, that I was watering them every day, but I stopped about a week ago. Do you think that there is anything I can do?
You situation sounds to me like a case of powdery mildew. If the plants are below hedges and under trees I might worry that they are not getting quite enough air flow. If you are watering so often and that water is not getting the chance to completely evaporate during the day then the foliage of your plants can develop the unsightly white fungus. It is not going to kill the plants necessarily, but it certainly does nothing for the aesthetics of your garden. There are recipes for a homemade concoction of water and baking soda (2 tbsp. baking soda per gal. of water), and a drop of dish soap for viscosity, and applying this as a foliar spray. That usually does the trick, even if you have to do a few applications over a couple weeks time. You may choose to do this in addition to lightening up on your watering schedule.
You are already watering your plants at the right time of day. Typically early watering allows for proper evaporation during the day, but again, it might be more an issue of restricted air flow. You mentioned at the end that you were going to water less. Did that help? From my experience, granted a couple hundred miles away, I have found that impatiens can tolerate a fairly dry setting and still perform well. Perhaps you do not need to be watering them every other day.