Is this a nectria canker on my trident maple?

[JRidge]

 

[rockm]

I do not think so. Lichens and coral spot cancer are common in many places. And even though the individual species might vary, the symptoms of coral spot cancer are quite clear and recognizable. Near the top cut you can see the fruiting bodies pushing through the bark, rather than it being something spreading over the bark. And all the way at the basi of the trunk you can see a darker zone in the transition between the area with pink dots and the healthy bark, which to me is a necrosis line.

But... Your tree, your collection.

I was going to say the dark stains visible at the cut site shouldn’t be ignored. They indicate to me there is some sort of tissue infection happening here

Similar to verticillium wilt. Don’t think ts that but interior staining like that at the cut site is typical of an infection that blocks transport tissues

 

[Cruiser]

It does appear to be nectria. The darkened side of the trunk looks like it was already partly dead when you bought the tree. The necrotic area is slightly depressed, which makes it look like a developing canker.





Here is lichen that looks similar.