With a melt like that. You should trim and replant the tops of your stems. You're typically not going to get growth out of those bottoms again. Every once in a while you will, but I think you're best to just trim it,and not rely on hopes of what night not happen.
I pulled out all the bare stem and trim off the tops and replanted them they are growing back fine some of those lower leaves are starting to get holy.
But its the new Red Ludwigia I put in to replace the dead stuff that is showing the stem root?