@ajm55555, there is no substitute for doing a little autopsy on your dead tree. If verticillium had been to blame you would have found dark 'streaks' in the wood (the tree would have suddenly died/'flamed out' in early spring, before temperature were well above 70F). If it was nectria canker, you would have seen orange fruiting bodies in late summer and/or early fall. If you drowned the roots despite using an inorganic substrate or overdid root pruning, death most likely happened soon after repotting. Etc. Keep notes and do an autopsy when death occurs.
I have a shin deshojo in my yard. Planted it there 10, maybe 11, years ago. There is another one 5 blocks away that has been then for just about as long and another pair about 4 block away for about 5 years now. All were 5-10 year old trees when planted and are thriving, healthy, beautiful, grafted landscape specimens. Mine gets pruned and air layered just about every year. I'm not sure that the owners of the others do anything to/with theirs.
I've had troubles getting layers established on their own roots and met with constant failure over a span of 4 years. After a respite, it now seems like a piece of cake to layer even though I continue to experience troubles getting the layers 'established' on their own roots. Last year I had three layers from the previous season and two of them died. I'm not clear on exactly why, but it is just like my past experience. I also harvested another 5 layers last year, that are all leafing out nicely this year (we'll see).
I've had one or more of 17 different varieties of 'Japanese maples' (a. palmatum, a. shirasawanum) in my landscape and/or in pots. I've killed 7 trees (total) in 3 of those varieties by my mistakes. One died because of a problem that wasn't apparent when I bought it. One was lost to nectria. My mistake with that particular one led to infecting two other trees (not sterilizing my pruners).
