I agree with TJ that it looks like leaf spot (I think TJ had a typo, it's spot not shot from my research) - It's a fungal pathogen, and I'm wondering if there are some fermented herbal sprays that include garlic, other aromatic herbs, nettles etc. that could be effective for this. I'm about to move from Oregon to Florida and my Holistic Orchard book by Michael Phillips is packed away. That would be a good resource to check out. Other than herbal sprays which can use friendly bacteria and microbes to combat the fungus on the leaves, I've read that removing the infected leaves from the trees and ground around them, and making sure the area has plenty of air circulation and sun will help to deter the fungus from proliferating. Best wishes, and do add some mulch if you can.. wood chips that leave about 10 cm of space around the trunk will help the trees roots grow strong, help the soil come to life, and make a situation where the tree's natural strength and immune system are better supported. Send me a PM if you want to chat a bit more - Pete