When I first looked at it,I thought it was Anthracnose, but if you re saying whole branches are dying, (if this is indeed the case), it wouldn't be this. I would need to know how many branches have actually been lost, and want to see a branch or two that is declining. These Maple trees are very susceptible to Anthracnose, and it appears much worse tan it really is. If left aloe, te tree can recover over the next year, but it is not uncommon for this to happen from season to season. It is also common for these trees to drop leaves around now due to dry stress. Leaves are dopping like crazy around here right now...especially off Maples.