Certified GKH Gardening Expert
This is often related to a fungal infection. You can cure this, but the old growth will never recover, and it is likely that there will not be much new growth in dead spots. But it will stop the spread of the infection, and new growth will be unaffected.
Wettable sulfur is the easiest treatment. If you fear that the soil is already highly acidic, then you may want to add just a little dolomitic lime, a quarter handful per tree, to keep the pH from swinging too low from treatment.