I see this type of possible infection during our periods of drought, especially on the maples thus causing Maple wilt. The classic symptom of water vessel restriction from the infected phloem tissue.
This kind of inconsistent browning of the foliage and limb death. I will take twig cuttings that are at least a half to one inch in diameter and cut the bark away. If there is streaks in the wood or discoloration, I will take the cuttings to the extension office anyway. The problem with our extension services here is there is no real experts in this field.......let alone the forestry commission.
It has been my understanding that trees with this disease.......if this is what it is, to keep the tree in proper health........watering, feeding and pruning of the infected limbs and twigs. Death may be imminent over time. More and more infected limbs and branches will become more evident as the disease progresses.
The only other possible thing could be Anthracnose in the later stages!!!!!