Japanese Maple problem
One of my Japanese maple's foliage is 'thin' this year. There are bare branches, especially at the top. They are usually red and this year they appear more green with some orange. (You can see the contrast with the one to the right of it in the pic I attached.) I believe the tree to be at least 7 yrs old. Conditions haven't changed as far as I know. It gets pretty close to full sun. I have never used fertilizer or pesticides on it. All I've seen on the branches is a spider and a ladybug. I don't see anything on the undersides of the leaves. The same thing happened to a smaller (8-9 ft) Japanese maple that was about 15 ft. from this one. It started three springs ago, and each year there were less and less leaves, starting from the top - sort of like it was going bald. By last spring it was dead. It looks like the same thing is happening to this one and I fear it's just a matter of time before whatever it is, will take out the one next to it. Can you help? Any suggestions?
Baltimore County Maryland
In general, Japanese maples are subject to many environmental stressors such as drought, poor drainage, too much moisture, temperature extremes, too much mulch, planting too deeply, soil compaction, etc. Also, with Japanese maples the bark can freeze and kill the cambium which can cause dieback. This is a possibility regarding branch dieback.
Also, in your photos, it looks like there are 3 trees are planted too close to the house and are planted too close together. There will be competition for moisture and nutrients and the trees will grow slowly. Also, It looks like a well cap is in the area which can affect root growth. If this is a well cap, it is not a good idea to plant trees this close to the well. It would be better to have shallow growing perennials in the area around the well.
At this point, prune all dead wood and see what you have left. You will have to decide if you want to remove the trees or at least several of them. Keep well watered during dry periods. In the future, plan for the mature height and width of the tree before planting.