Doesn't look very good :-( Where are you located? And how was your winter and spring weather? Any late hard freezes? Drought stress last season?

JM's can often recover from late cold damage but not sure that is the case here. The random leaf development makes that somewhat unlikely. Are there viable buds on the bare stems?

There are also various pathogens, generally untreatable, that can also cause random dieback. I might wait awhile to see if the tree developes more foliage or reflushes from any viable buds. If you see nothing or it gets worse by mid to late June, I'd take in samples to your local extension office for a proper diagnosis.

Southern NY, not a particularly bad winter, watered regularly with sprinkler system, some new growth low on branches, thanks

Half? I'd wait too, but I think That is too far gone. If you were feeling adventurous, you could chop it to about a foot and a half or so, and see if it will back bud and start over.

New growth

Thank you