I'm not following quite this. I don't think a Geranium (Pelargonium) is likely to have lichen. Do you mean mould? And they are not known for producing fruit. Secondly, I don't get the 'Orange tree of the same species' thing. Do you mean an actual orange tree or an orange Geranium? Amancayo seems to be Plumera .

Pelargoniums come from S Africa ie a warm dryish climate. Colombia afaik is a warm moist climate. So they are likely to suffer from all sorts of moulds and fungi. I can only suggest you try to increase air circulation around the plants. Remove diseased foliage and don't water overhead - although if it raining frequently there's not much you can do about that. They also prefer lean soil rather than high nitrogen so the manure will not have helped since it would promote sappy soft foliage which is easy prey for pests and diseases. So in short - stop fertilising, don't water and increase air flow.