Tuning up the orchard.
All maladies, whether affecting human, animal, herb or tree, are the result of mineral deficiency and malnutrition in some form. Modern technology has disguised most of this through heavy doses of inorganic chemicals resulting in the absence of true health in any living entity. Chemicals kill enzymes. Enzymes break down soils, releasing the nutrients that are there, thus feeding the plant. Any plant can be made to appear healthy, for a while, by chemical application alone. The time for that is past.
Diseased trees may or may not be too far gone to be salvaged.
If you want to address the "root" of the problem, organically, you will have to start from scratch. You will have to feed the soil, and the soil organisms, so that they can properly feed the tree. One thing to keep in mind is the vast difference between harsh, man made chemicals, and naturally mined minerals.
Many fruit trees suffer from a simple boron deficiency. A very light sprinkling of common borax around the drip line will eliminate that possibility.
A thorough digging up of the surface soil around the tree and a liberal working in of good, finished compost is the next step. Mulch is a valuable aid for orchards, locking in moisture and offering cover and food for earthworms.
Worms do wonders for soil permeability, tilth and mineral distribution, not to mention the incredible boost that they give to enzyme activity. Always be sure to rake mulch back six to eight inches away from the trunks of your trees, to discourage root and trunk boring worms from taking up residence. Trees don't generally require much lime, but a soil pH test could be telling. However, rich compost will balance pH in time and will cushion the effects of an imbalance once it is thoroughly incorporated into the soil. A sprinkling of wood ashes will naturally boost potassium and offer many trace minerals. Finally, a liberal working in of a super mineral supplement such as kelp meal will assure that most, if not all mineral needs are met. After that, patience is your ally.
Natural "cures" take time. But they are like the stone house that took years to build, compared to the stick hut that took two days. How much effort are you willing to commit to ?
This applies to all soils, and all plants and livestock. Feed all soils thoroughly, yet in a balanced fashion, and they will feed you beyond your most optimistic expectations.