Mel M Kelly wrote:
Check the stem close to the ground and see if there is a bad spot with
some stuff ozzing out. Could be a cucomber borer.

Yes. Squashes and cucumbers are likely to get borers. I usually
sprinkly a little rotenone around the new plants and later on, along the
stems.

If you do get a borer, you'll see orange stuff like sawdust. Take a
pocket knife and split the stem until you find and kill the borer. If
you bury the stem at the split, it may send out roots from that point.