I tend to err on the side of caution when presented with that much potential dieback and take a wait-and-see attitude about removal :-) Sometimes there are reasons why a tree does not leaf out uniformly.

You don't say where you are located so no clear idea if this is winter cold damage, late freeze damage or something pathogenic. What do the buds look like on the unleafed portion? Are they brown and dry or still plump?

If the buds are dry and brown and it hasn't leafed out by the end of June, I would go ahead and remove. And be sure to sterilize your pruners between cuts in case it is something pathogenic.......you won't want to spread it around.

Here’s a better picture I am in NJ and the other JMs have come back strong This one is the lagard

Can the Forum please confirm the best method of sterilizing Pruners ?

I prefer Isopropyl alcohol. It isn't corrosive, dries almost immediately, no need to rinse, and is effective at removing resins and sap. I buy boxes of pre-packaged swabs to make it easy.

I also use Isopropyl alcohol and the pre-moistened wipes with alcohol.