Perhaps water stress, as in not enough. If the tree is well-established, it may be a temporary thing and will stop when the weather becomes more reasonable.

However, it would be wise to check the soil -- is it wet, moist, or dry? If dry, water thoroughly.

I also have a maple that seems to be in terrible distress. We have had a strange spring/early summer full of wild wind storms, unseasonably cold temps alternating with unseasonably hot temps, huge thunderstorms, then a week or so without rain.... The leaves on the tree are spotted with brown and many have already fallen from the tree, littering the yard. It looks like autumn in that spot of the yard. What should I do? It is a large, well established old tree.

My Japanese maple (bloodgood) is also ailing. The tree has lost almost all of its leaves. The leaves are curling and falling off, and I am wondering what can be done for this tree. It has been a very rainy spring, and we had extreme fluctuations in temperature, a warm spell, and then a frost. I brought some of the leaves to a garden center, and their recommendation was to fertilize the tree. It continues to lose its leaves, and there are very few left. Does anyone have any idea what is wrong, and what can be done to save this tree. I planted it five years ago, it is about ten feet tall and it is the focal point of my garden. I hate to lose it, and would appreciate your knowledge and advice.

I can't answer your question not knowledgable enough about disease but one thing I wouldn't do is eiither fertilize or heavily water( unless it's bone dry ) a tree in stress ...It's a kin to pushing someone off a cliff...you will hurry it's demise IMHO David