Came infected with pseudomonas, was grown in soil infested with verticillium or the new site has it, new site does not drain adequately...dieback and decline of Japanese maples is not rare. One expert in my area recommends against additional plantings of these as he has seen so many that are blighting off.

The Garden Center that I purchased gets this cultivar Koto no ito in as B&B. Still same after 3 yrs. Agree that this may not be a good choice
Was considering another maple but maybe a different cultivar. Acer p Scolopendrifolium. or maybe Acer p Aoyagi.
I can amend soil to improve drainage.
Your thoughts

I have talked to 2 maple collector and both have said Koto-no-ito is a hardy plant so there may be cultural issues involved.

One of the local nursery owners I talked to about this type of a problem, slow decline with some branch lose said many think it might me due to the wet springs followed by dry summer periods we have had the last several years as japanese maples are from an area with more steady moisture. He also said his maples that are in an area that gets even moisture are not showing the problems. David

If it is verticillium or a similar soil pathogen, a replacement will probably succumb in a similar manner. These diseases live in the soil and any plant that is not resistant will be affected.

Personally, I don't know if I would invest in another expensive cultivar of anything that might be damaged by soil pathogens. Perhaps an accent plant that may be more resistant in your area should be used.

However, you could take the risk and assume that it is a drainage issue that could be fixed.

Bad drainage is corrected by putting in drain lines.

"Use no soil amendments except in very specific conditions of raised or amended beds for plants with very limited root systems. If the existing soil is very poor, remove and replace with good field soil or place at least six inches of good field soil on the surface. However, you should match soil types as backfilling with a good sandy loam in a heavy clay will serve as a collection point for water and the roots will suffocate. Soil amendments in a small planting hole do not assist plant establishment. It is better to use the amendments as a mulch. The only exception is where the entire plant root zone for many years can be amended."

--C.E. Whitcomb, ESTABLISHMENT AND MAINTENANCE OF LANDSCAPE PLANTS

I've heard there is a problem with sloppy production practices resulting in Japanese maples being put on the market with systemic pseudomonas infections. No amount of fiddling with the final planting site will cure that.

Also as has been stated gere many times once a tree kapuits from any questionable pathogen or you are not sure of cause DO NOT re-plant in same area as a precaution against soil born gargbage I have the same probblem with a Sieru I just about whipped it last year but this horrible WET cold spring and my laziness to get it sprayed has put it again at risk ...my Psuedo is on the trunk and some branches.. I do so love the Scolopendrifolium mine withstood most of the 10 day mid to lower 20's virtually unharmed and uncovered and in a really exposed area ...I did cover it for the 19 degree night ... It actually looks ok and did the best of any larger tree that had leaved ...the Scolopendrifolium Rubrum ditto...both highly recommended for hardiness and beauty..David

Update
Dug up the maple. Although the tree was planted in a bed mounded with about 12" (delivered) topsoil, the soil was very compact. The root structure for a tree that was once 5ft tall and planted in the spot for at least 3 yrs was not well developed. It was very easy to dig out and remove. There was new growth only at the bottom 12- 18" of the tree, the remainder was dead. The branches were not black or unsuually discolored.
We had rain here about 2 days ago - and the soil was slightly damp - I would guess that the dainage was poor.

What was strange was that in the same bed the owner had three small purple rhododendrons that were blooming and looked great.

One more thing - I think that the owner did not water this tree through out the summer, when there may have been dry spells.

Did not replace with a maple -

Thanks for all the help ------ Mike

Manufactured soils sold here as topsoil often silty, with a flour-like texture. I've taken a typical product and shaken it in a jar with water, had a high percentage of fine particles settle out. When I finally dumped it out after a quite a bit of time it seemed to still be separating into layers, not enough of them coarse particles. Note that Whitcomb (above) said "field soil", as in real naturally-formed soil. Here in the land of glacial till there used to be one or two places where you could buy lakebottom or similar attractive natural soil, now I think for the most part all you can find is "black dirt" (decayed peat or other humic material).