Zelkova sick trunk?

[konn]

Hi all,
do you know what makes the trunk of my zelkova peel off like that? The affected area was much smaller 2 years ago when I got the tree. It has been expanding gradually. I have been spraying with copper based pesticides but with no effect at all. Does anybody know what it is and what I can do?
Many thanks.

 

[Shibui]

Do you rotate the tree or is one side always facing the sun? Sunburn is one possible cause of damage like this, especially when it has such a small canopy to shade the trunk and roots.
Physical damage can also cause dead patches like this - tree falling off bench, being hit with another object, etc. The damage does not show up for many months and we've usually forgotten about that incident that may have caused the damage. You mentioned the tree already had this damage when you got it so you won't know what may have happened to cause it before you bought the tree. In the early stages it can take months or even years for the full extent of damage to show up.

The affected area was much smaller 2 years ago when I got the tree. It has been expanding gradually.

Is it getting wider or just up and downward?
Scars like this do not usually spread but that section between the 2 dead parts probably has very little sap flow now so is likely to die off slowly to form a single scar.
Can you get a good clear, close up shot of the edges of the dead area to see if there's any callus forming at the edges of dead/live.

I have been spraying with copper based pesticides

What pesticides are copper based. Copper is the base for some fungicides but I don't recall any pesticides using it. Copper fungicides usually used to treat leaf infection. I doubt it is effective on infections in trunk and branches. Phosphoric acid fungicide is systemic and more likely to be effective if there's a fungal infection in roots or trunk but I doubt that's the issue here.
In any case I doubt this is pest related. Possible but not likely fungal.

 

[konn]

What pesticides are copper based. Copper is the base for some fungicides but I don't recall any pesticides using it.

Sorry, I meant fungicides.

It is getting both wider and longer. Mostly longer, expanding towards up and down (see the blue arrows). When I first got it, the upper dead part (between the two arrows) did not exist. The lower larger part was around half today's size.

During the first winter I left it outside and it was exposed to temperatures around 0 degrees Celcious. At some point I realized I needed to protect it more, and I got suspicious about the cold possibly causing the damage to the truck, and I brought it inside. This winter I kept it inside in a cold room (lowest must have been around 5 degrees Celcious). During the last summer I maybe have turned the dead truck side towards the sun once or twice, yes, in the hope that the sun kills the infection I guess. Did I make it worse?


Is there anything I can do now? How would you recommend I continue with the tree?

 

[TrevorLarsen]

First I’m no expert about if this problem will spread or not, or what is causing it. But if it were my tree at this point I would be thinking of either carving into a hollow trunk tree down the road. Or making it into a raft style tree, that is another option I would consider.

 

[Deep Sea Diver]

Run into something akin to this before on Zelkovas.

Might be something like Chinese Elm Anthracnose

Best
DSD sends

 

[Shibui]

Sorry, I meant fungicides

No problem. There's often translation issues where English may not be someone's first language. I just needed to check we were both on the same page.

I can't see any healthy callus around the edges of those scars so it appears the tree is not healing as it should. That's not good and your observation that the problem is getting wider and longer confirms that there is a problem.
Normally trees are able to contain the dead sections and begin to grow new bark over the top so a dead section is no real problem but that does not seem to be the case here.
I have not come across this problem in nearly 40 years working with plants and bonsai in particular so I can't offer any solutions but you could explore the possibility offered by @Deep Sea Diver

It may give you some comfort that I find Zelkova challenging here too. I've lost many trees through our winter though it is not particularly cold here. Seems to be a fungal issue related to cool, wet conditions here rather than wounds not healing. I only have one large, old bonsai zelkova and one half of that tree has recently decided to die.

Provided the problem doesn't seem to be spreading to other trees I would just monitor the progress and if the tree survives try @TrevorLarsen advice for a hollow trunk styled tree.

Sorry I can't be more helpful.
Good luck with the Zelkova.

 

[konn]

Thank you all anyway.
Well, I think I would like to try to chop the trunk below the infected area. That would be 2 cm above the soil. Do you think the tree will survive? If so, when should I do it? The tree now is just waking up, buds are swelling and small leaves appear. Or should I wait for middle of the summer, maybe while the tree is growing fast?