It was suggested "Exact diagnosis can be made by taking a sample to your local extension office but if it is Phytophthora (or another root invading fungus), there is little you can do now." If such a sample is brought to the Extension Service office, please call ahead so that the Master Gardeners have time to locate information as to how to sample the soil & the affected root tips. Also know that a fee is charged, the precise amount depending upon the test to be done -- fees for the OSU Plant Disease Clinic begin at $40.00. Beyond that, I doubt this will be an easy diagnosis. I'd consider multiple factors potentially contributing to the problem: 1. Because OP said s/he "paid quite a bit of money" I suspect it is a sizable specimen. If so, post-plant irrigation is a critical factor in survival. All transplants should go into evenly moist soil, then the rootball should be supplied with more water than the surrounding area during the following months. Failures of recent transplants typically are due to water -- either too much or too little. 2. The sudden very cold weather in December, without snow cover, damaged & even killed many plants hereabouts, including those which survived 10 years or more. 3. The tree is a recent transplant. As such it is more likely to be damaged by cold than an established tree of the same kind. 4. Dormant roots are less susceptible to water damage than are actively growing roots. 5. In general -- and yes, exceptions exist -- root rot results in entire tree failure. 6. It's nigh to impossible to diagnose root rot by looking at dead branches and/or browning leaves. 7. And perhaps most critical, multiple nearby specimen maples are in potential jeopardy if the problem is indeed soil-borne, such as Phytophthora root rot or verticillium wilt. So, I suggest pinkswine consider having a certified arborist or two come for an on-site evaluation. To locate a certified arborist, look in the Yellow Pages under the heading of Trees or something similar. Ads for companies with a certified aroborist will either have a statement or small rectangular logo stating such.

They often are, this cultivar being even more prone to disease problems than many other Japanese maples. And, yes, digging a hole out of a clay soil and then replacing the soil with compost and top soil is an excellent way to collect water around a tree and kill it. This is about the main reason to never amend planting hole back-fill soil. All Japanese maples must have excellent soil drainage at all times.

I love it. Great story! Dax

I'm not an expert but I have a coral bark maple that has done the same thing. The first time, I cut the branches out, thinking it had to be a problem. Then I saw an episode of an Erica Glasner "Gardener's Diary" on HGTV where she visited someone with many Japanese maples. As they walked through the garden he pointed out a maple that had branches with the same larger leaves and said that the next year they would be the proper size. So, the next time it happened, I left them and sure enough, the next spring those branches had the proper sized leaves. I don't recal the variety of maple that was on the show. I have around 15 Japanese maples and the coral bark is the only one that has done this. Hope this helps.