AusBonsai

I have a stout persimmon that is changing from a trunk to a tree [ie, getting branches]. Currently it has 4 branches including the header. One branch, the back branch, is still green but thickening rapidly and carrying a number of healthy leaves but it wilts in hot weather. The soil is moist, I do a second full water, turn the tree so the branch gets more shade but it wilts and stays wilted until the sun eases. There is no problem whatsoever with the connection to the trunk, there is no damage to this branch so there's no visible water flow inhibition. Why the wilting? Has anyone experienced this problem? I am hoping when the apex fills out there will be shading branches to ease the sensitivities or maybe, when the branch hardens off this will ease but in the meantime, I need that branch where it is and am worried about it.

Can't think of anything at the moment but a picture of the severity might help?

could be a problem below the soil with roots on that side of the tree has it been root pruned lately or repoted

Check for borers. Look for sawdust on the soil surface or near the branch on the trunk.
Jerry

The tree does not have any pests or diseases. It had a very hard root prune in August as there were 5 thick stubs under the soil that had to be removed if the tree was ever going to sit in a reasonable pot. At that time it had two small branchlets only so there wasn't much life to support. After the initial wound licking it has grown robustly, including replacing an important branch on the tip of the reduced branch that I inadvertently knocked off when root pruning. As soon as the sun eases the wilted branch fully recovers. And so we go from day to day.

I would say it is struggling to draw enough up from the roots to sustain itself in the heat.
There was a recent quiz on one of the blogs about why growing tips droop when the soil is moist. I was interested in this is I often had the trouble with fresh growing tips of the hornbeam sagging. Very healthy looking growth and the hardened leaves where fine but the tips would sag as though it was dry.
The answer was that it was from a tree in a harsh environment and the surface roots had been scorched. Hence there was not enough roots to supply enough moisture. I was not happy with this answer as I figured it was a one of event that was being put in a too broad a sense.
I have watched this in my trees intently this year and I have found the most robust root systems of Hornbeam and others, say ones that only needed a slight trim, are almost non affected by this. A collected hawthorn although looking exceptionally healthy and in a shade house often has the fresh tip droop in the heat of the day. So I would expand on the quiz answer I was given and say the growing tips will droop when the roots are struggling to supply the tips enough.
Now I do not panic when this happens as the trees grow on in good health but when I see a tree that has done it before not doing it I figure I am doing an extra good gob.

I believe with the root pruning you have done the roots are just at a point where it is only just keeping up with moisture supply for the tree. As this is fresh growth it is most affected where the hardened growth can still hold it's structure.
It may be a good idea to move to a cooler spot if possible and be very careful not to over water but basically do what you can to help the root system gain strength.

Thanks... that was my thinking considering the severity of the root clean up that I had to do. Today is over 30 and I have put it on a milk crate under the cape honeysuckle where it will get a bit of direct sun but not near as much as on the benches. As the tree is healthy in all other respects and throwing out new and lovely leaves, even on the affected shoot, I am mollycoddling it as necessary and hope that it will soon grow enough additional roots to carry the load. Also, I will start doing alternate weeks with Super Thrive to aid root growth.

Try some fish emulsions as well as the condition the soil encourage root growth and fine twiging on branches I allso use root hormone mixed in a watering can mild