Could be downy mildew. It has been devastating in other parts of the country
I'm in Virginia Beach and ours are horrid also. Too much rain this summer and the mildew is killing everything.
Our growers/nurserymen in the ATL area sounded the alarm back in January of this year to alert homeowners and gardeners to refrain from purchasing the shade-loving common and double-flowering impatiens. They think the problem was discovered in the UK about 5 yrs. ago, and the water mold/fungus will stay around for many years to come. About August is the time when you will see them literally collapse within a week's time, for no obvious reason. Spores from the fungus will remain in the soil for several years. You can plant successfully New Guinea and Sunpatiens; the fungus is species specific.