remove it ... who knows how long it might live.. but it will die.. sooner or later ... the damage could have been pre-existing at purchase.. but did not manifest itself until after the stress of transplant ... or even potting or ball and burlap in the first place ... that damage is WWWAAAYYYY!!!! beyond sunscald ... it may have been part of the equation.. but it is not the sole cause ... almost looks like a beaver came by and took a nip .. and i will presume.. that aint possible.. lol ... boy it looks like you have a nice sized property there ... as to your groups of 3 ... whatever ... i know the theory ... i usually ignore such ... i would have planted the three more around the yard [i have 5 acres] .. to create a backbone for the larger landscape.. rather than investing the cost of three ... in a small area ... why are you insistent on a grouping of 3 ... thinking outside the box you are in.. get rid of the sickly one.. and move one of the others 50 feet away .. and look for some other plants. .. to fill in around a given single plant ...??? the problem with groupings.. as you have learned.. is when one of them dies .. and then you are left with a lack of balance.. and two usually doesnt work ... so you are left with dealing with 'filling in' ... and trying again.. on what might be a plant that is hard to deal with ... think outside your box.. and good luck if there is any chance.. that there is a warranty involved .. exercise it ASAP ... ken

Thanks for the advice. I had no idea how to "scrape" the bark seeing as I don't have long enough finger nails to do the job. I will certainly make a mental note for next time that I don't have to go so deep. I love trees in general and don't like the thought of harming them. I'm happy to hear what you've shared with me. Thanks again for your expertise.

Probably. I think you need to fully girdle the tree to kill it and even then some trees will scar over and heal. Stiil, a wound like that might call for some protection from borers and other opportunistic dangers.

May I join in this thread about my two new mandarin trees with bark damage, as well, or should I start a new thread? I got two little Page Mandarins and didn't notice when I picked them up that the bark is damaged on both. New bark is growing into the bare space. The damage goes from the root stock to the tree itself in one long strip on the one and the other one is the same except not so long a strip and there's another little spot on the tree trunk. I'd post a photo, but don't know how and my husband is away on his work hitch. I was wondering if there is anything I should do clean off the dark mildew that is on the tree trunk and that has discolored the wood inside. I'm not losing any money on them and they have lots of leaves, but most of the new growth is full of leaf miners and they look awful, but are still green. They're not losing any more leaves than is normal, from what I can tell. I wish I had found them sooner in the season so I could give them some Foliage Pro to help them. The bark that is filling in seems to be healthy-looking. Thanks, Vivian