The soil appears poor and compacted in the first photo. The tree needs repotting badly, but to do so now would likely kill it. Even those experienced in out of season repots would be reluctant to repot now. You can plant out and lift & repot next spring, or plant entire container & repot next spring. Both of these options are better than potting up, as you'll create dissimilar soils in the container & one soil will always be too dry and the other too wet.

Al

Appears to be a rather stressed specimen of coral bark maple, 'Sango Kaku'. These are rather prone to pseudomonas, specially under stressed or excessively wet conditions. Pruning out affected portions (disinfect pruners after each cut) can retard development and spread, but this plant should be out of the pot and in the ground to reduce stress. I'd also be concerned about the unfavorable growth pattern of the limb that is twisting around the main trunk - if this tree survives, that will only be a continuing problem down the road. I'd remove it now while the tree is still quite juvenile.

Thank you both for your responses!

tapla--I'm going to have to study your comment; I'm such a novice that I don't even understand the terminology you used (plant out vs plant up). But it sounds like I shouldn't do it this season anyway.

gardengal48--Do pseudomonas put my other plants at risk, or are these bacteria present everywhere and only susceptible plants get them? I don't think it would be difficult to remove the twisting branch, as it does not have much growing on it. On the other hand, it seems like every single branch has some healthy leaves and some withered leaves; it's not limited to one area. Should I remove just the withered leaves at their stalks? And how would I best disenfect the pruners? Do they even make pruners that small?

I apologize for the questions. (I told y'all I was a novice.) I guess maybe I should just hire an arborist to see if it can be saved.

Thanks again for your help.

"Plant out" (in the ground) is what Pam suggested & is your best bet. Potting up is simply moving the plant to a container of greater size & soil volume. I should also have mentioned the limb entwined around the main stem - Pam is, of course, right in suggesting you remove it in the near future.

She knows her stuff, so perhaps she can suggest a suitable fungicide, other than the Bordeaux Mix I would use - if you're of a mind to use one. Trees that are not stressed are usually able to defend against this bacteria, another reason to get the plant in the ground where it can recover some vitality.

Al

It's a bacterium that's pretty difficult to control. Rather prevelent here in the PNW as our weather is an ideal environment for the pathogen and it can decimate a good number of nursery crops. Recent studies by OSU have shown that there are numerous variations of the pathogen and that many strains have developed resistance to the typical controls, usually copper or streptomycin. Copper, like the Bordeaux mix, is likely your best chemical control or a similar product like Microcop. Application should be begin in fall and again early in the season before budbreak. It is likely too late to apply now that the tree is in leaf - J. maples are rather sensitive to sprays on their foliage and copper in particular can cause a phytotoxic reaction.

I would remove the blackened foliage and trim back any leafless portions to a healthy node. Watch for stem discoloration and as you see it, prune out below it. (And yes, good pruners come in all sizes :-)) Disinfect the pruners with something like rubbing alcohol or bleach - Lysol spray is popular at my nursery. Plant it in a good location as soon as you can and keep an eye on it. A young tree in decent growing conditions could outgrow it, but nothing is guaranteed.