Cut out anything dead, and that appears to be the whole of the old stem. Since it’s dead the question of doing it while it’s young is irrelevant. When you choose to cut it can’t affect the tree.

It needs to grow out for a year before it becomes obvious where your pruning cuts will be. It will be very bushy looking during that period, but that's ok. When it gets to be 6 feet or so, hire someone skilled at pruning trees-who can make the right cuts to get it looking like a nice tree. It will only cost you $60 or so, and well worth the money. Its way too soon to make any cuts, especially going into fall/winter. Also put some cheap wire fencing around it - for deer protection.

I kind of agree with both of these. You can always remove dead wood. Anything that snaps easily is dead and can be removed in October, no problems. Just don't cut back to living wood right now, leave that for spring.

Later on, follow Tom's advice or, if you're confident pruning a young tree (I am, personally), DIY it in spring of 2022 or so. If you're very good at tree whispering, you might be able to see the main branching in late spring of 2021 as the hints of what's going to happen are already there, really.

next ... do not cut off any live growth.. this time of year.. you dont want to stimulate new gtrowth.. goign into winter ...which might end up just fine with you... so be patient ...

next.. not many things die from a bad pruning.. no matter who does it ... so this isnt all that surprising ...

next ...

cut off nothing that you cant get to easily ... you dont want to damage new growth .. with trees and shrubs.. there is no real hurry ..

next ... do not cut off any live growth.. this time of year.. you dont want to stimulate new growth.. going into winter ...

next ... if you can find someone who will drop good work to come to you for 60 bucks.. let us know ... im thinking that idea will not come all that cheap ... but that depends on where you are ... unless you join a garden club.. and someone will do it for free ...

but even then.. its not all that a big deal.. in a year or 3 .. you can do it yourself ... its not hard with a good pair of hand pruners.. which might also cost you more than 60 bucks.. lol ..

plan on killing and removing the grass around it and then mulching.. just on principle ...

eventually you can train it to one trunk.. or more shrub form.. thats all in the years to come .....

do not fert it in fall ... we want it to go dormant .. not get all juiced up .... [your pic doesnt look like a warm zone area ...]

ken

I blew up your pictures. To me there does not appear to be a new trunk, but several branches on the old trunk.

I would cut the dead part off, about the base of the "Y" previously of the old cut and the old main trunk. It looks to be about 12 to 14 inches up the old trunk.

I would do nothing to the tree for a couple of years to see want the tree is going to do. Once you see what the tree wants to do, trim accordingly.

Also leaving the "bush" alone will give the Deer, etc. something to eat while the tree is making up it mind.

It appears to me all that growth is coming from the base and are suckers from the rootstock and not your original cultivar.

tj

I wouldn't cut any living sprouts for a couple yrs. The tree was hurt badly and the root system needs all the leaves it can get for at least a couple yrs before hacking away at new growth.

okay thanks...there is fencing around it, as shows lightly in the photos. I think I may leave it alone for the fall and winter and see what has happened by spring. If it's too big I'll get a professional opinion.

I'm sorry to be a downer, but I wouldn't count on that chickenwire fence keeping Bambi off your magnolia. Something heavier would be a better bet, I think, and some T or U bar fencing posts to hold it steady.

We have deer in the pasture almost daily and its worked so far. Plus we have plenty of construction machinery in the yard around the trees right now.