The sunken area at the base appears to be to be canker. Had to remove a Ukigumo JM earlier in the season for this very reason. I have seen allot of this over the last few years. Have seen allot of it on crabapples, Japanese Maples, and other maples. Plants sometimes beat the pathogen, sometimes not. If they are going to beat it, then expect to see callus to form around the edges of the sunken area. Even if the callus forms, it is far from certain. Once the tree goes dormant for the winter, the canker will often gain the upper hand again. However if the callus does not form by end of summer, then from what I have seen, it's almost certainly a matter of time before the tree is killed. As for how your plant became infected, I suspect that a number of low cost and/or large scale producers have gotten very careless over the last 5-10 years. There has been allot of apparent disease increase in allot of other plant groups as well over the same period (Aster Yellows seems to be everywhere anymore, to the point it's getting rather difficult to get disease free coneflowers, saw this Saturday at the largest local nursery). I'm sure part of it is due to producers having a difficult time the last several years, therefore cutting corners, poor training, poor enforcement, less responsible labor, etc. But also Big Box Store has little incentive, as they know Q Public is unlikely to know anything about disease and will be back again next year to buy another one. Arktrees

I'm in zone 5 Ottawa,Canada. Zone 4 for you in the US. They used to say you couldn't grow J.maples around here. But for 20 years I always could, and have never lost any, except 2 variegated ones. I have about 25 varieties, a sort of J. maple forest in my back yard & I am running out of room. Good thing they are dwarf trees, unlike our native maples that grow to 50 ft. I wholesale them from (grown in)BC, zone 7-8. They do not loose hardiness by grafting and propagating in a milder climate. The hardiness is built into the plant. I will say that they can sometimes be slow to establish, and this is the important part. Any tree should be planted early and well cared for in the first season, so it is well established going into it's first winter. I don't believe in bare root trees doing well, too slow to establish, or over wintering in a pot. They should always be planted in the ground and well mulched. I do think they prefer a more acidic soil. Ours is neutral approx. 6-7ph, so I spread sulphur everywhere every couple of years to acidify a little.(I don't like pink hydrangeas, prefer blue) I saw a study once, out of U of Michigan I think, where when they tested plants, and they found that plants growing in acidic soil seemed a little hardier than the same plants growing in more alkaline soils. In the past I have used geo-textile fleece as a winter cover for the first few winters, but snow makes a great insulator as well. I get a bit of tip dieback sometimes, but it doesn't matter since they grow back very well, as if they were pruned. There is a sort of wilt going around in J. maples lately, others have noticed as well. It doesn't hurt the tree, it just attacks some of the newest growing tips as they are finished flushing out in summer....sort of self pruning. We regularly get to minus 22 celcius (-10 far.)here most winters, with minimal problems. Even with last winter, the worst in 20 yrs., there were no losses. The only damage I ever notice is the heavy snow pack in spring, will sometimes crack the weeping types as it weighs them down and melts. Variegated types do seem less hardy, possibly due to the fact that variegation is a mutation and therefore weaker. Red and green types are perfectly hardy. They all seem hardier as they get older. thanks, Rich

A certain amount of dieback is to be expected. But this is typically just the odd branch end or smaller twigs here and there. If there is a significant amount of dieback, then it may be the problem is not related to normal growth patterns or weather/cold damage but to some other cultural condition or disease pathogen. Without seeing exactly what kind of damage we are talking about, we are just speculating on a) it is normal or b) the symptom of something more pernicious.

get out the scissors ... and snip them off.. wrap them in plastic.. burn the lot.. and bag the ashes.. and drive them 60 miles from the house ... and be done with them .. the tree is gorgeous.. and way under-potted.. either get it in mother earth.. or put it in a bigger pot until the next proper planting time.. since it is most likely severely root bound.. i would probably recommend some severe root pruning.. but again.. i would do that when it is dormant.. which is the next proper planting time ... ask in the tree forum if you want some further info in that regard ... ken