Could it be borers? Check the stems around the point where the dead leaves start and see if there is a larva inside the stem. My grandfather (after cursing! LOL!) would cut a small slit in the stems of his zucchini plants and remove the larva, and the plants continued to flourish.

{{gwi:5901}}

No sign of borers that I could tell. I have dealt with squash vine borers in zucchini plants - those have larger diameter vines and the grubs are about 14" diameter. I sliced open the cucumber vines and didn't see anything inside. The insides of the healthy parts didn't look significantly different from the dying parts. I did find a few striped cucumber beetles and understand they can cause bacterial wilt. Can wilt kill the plant from the middle up as I am seeing?