I am not an expert in fruits but I have managed diseases in vegetable garden without using any synthetic products. If I were you, spray Zerotol late in the evening when the light is dimming and it has all night to act, this would control pathogen that is on the surface. Later in early morning before sun comes up I would spray revitalize concoction in double dose (with some molasses and you can exclude fish fertilizer if you find it smelly) and let it overwhelm the bad pathogen. Do this for a week and see the disease is under control before going to chemicals.
Hydrogen peroxide mix,