Mildew on azalea leaves is often the result of dry soil and crowded plants. A fungicide spray with Sulphur will help fight mildew on rhodies and azaleas and good fall cleanup of any fallen leaves will help to prevent reinfection. Perhaps if you remove the most infected plant the extra space and air circulation will help prevent this fungus among us from spreading. Once the mildew is so bad that the plant starts to wilt it is too late so save it. Keep growing, Marianne Binetti