I have 3 Japanese Maples that have been planted for over 10 years and have rarely shown signs of stress. I believe that two of the three are of the "Bloodgood" breed, whilst the other is some type of generic green-leafed Japanese maple.

The green-leafed one was the first to show symptoms, which included foliage dying at the extremities of the tree and collar rot. This specific tree I had not payed much attention too and thus wasn't entirely surprised that it had developed ailments. Upon digging, I found that it had pretty bad crown rot problems too. I kept the crown exposed to let it dry out, and then treated the rot with a mild solution of Clorox and water (1:20) over a few weeks. It is starting to show signs of recovering.

The second tree to show symptoms was one of the Bloodgoods. It started to lose leaves around the periphery. I dug around and found that most of the roots near the crown were okay, but a few 1 inch and 2 inch roots a few yards from the crown that had breached the surface were showing signs of decay. This is one of my most prized trees and was very vigorous, so I treated it with the same Clorox and water solution, along with replacing some of the topsoil with fresh compost. It is still in decline but the rate of foliage death appears to be declining.

The third tree is the one being referred to in my question. It has been extremely healthy throughout its life and has a beautiful branch structure. It seeded relatively early this spring/summer due to the warmer than usual weather here in Northern California. The seeds are finally falling off, but I noticed some red splotches on the leaves at the extremities like the other Bloodgood Japanese Maple. Upon closer inspection, it appeared that the leaves were crinkling up and dying. I dug around but found no symptoms of root rot. There is nothing abnormal about the crown or trunkline either. There is some die-off of internal branches, but that is relatively normal for a Japanese Maple of its size and age. So what is wrong with this third maple?