I believe it's wilt injected into the leaves by the stripped cucumber beetle. I've only been using County Fair Cucumber seeds for many years now, since they are resistant to this beetle and the wilt they cause. This is the only way I can have cucumbers.....is to use that variety of seed. Maybe others have an immediate solution for you, but I fear it will happen quickly to the rest of your cucumber crop. Look for those beetles and get rid of them. I don't use chemicals, so killing them is about the only solution.........and do patrol several times a day. Sorry!

P.S.........and make sure that particular stem didn't get pulled out of the ground.....OR......look at the bottom of the stem for signs of a squash borer that has injected its eggs into the stem. (They grow up in there and destroy the stem). Last year I began to have them for the first time in my cucumbers, and it does cause the whole stem to die. So.........it's one of the above possibilities. There's lots of info on this site for dealing with squash borers. Good luck!

My two cucumber plants are wilting too, one vine branch at a time more or less. Just before they grew any cucumbers. Frustrating, wanted to try at least one.

Yep, mine too -- looks like OP's pic. In my case, I don't think it's squash vine borer, since the damage to one of my plants started soon after transplanting, in early to mid June -- a bit too early for SVB damage up here. I have seen what I think are cucumber beetles out there, so my money is on that. I'm down to only one cucumber plant left, was showing no signs of wilting until I looked this afternoon -- sure enough, one of the stems is starting. Sigh... At least I got a few cukes already this year. I grow them for DH anyway, I'll eat them but don't really love them, but dang can he make a mean cucumber salad, quite a few different kinds. So that's a disappointment.

Ill have to check for damage do these beatles also affect beans? because my beans are getting absolutely ravaged

It's hard to believe how quickly those spotted cuc beetles can infect the whole stem. Like I said, it got so that I couldn't grow cucs at all, and I love them. So I discovered "County Fair" cucumbers. They are called "bitter free". It's hard to understand how that works, but apparently the cucumber beetles don't like it. I think there's another similar type of cucumber variety called something like "Little Leaf". I tried that one year, but didn't like it as much. There's no way I could have cucumbers ever, without the County Fair variety. They are pickling, but they can get pretty big.

Last year my cucs struggled through the summer, with tons of squash bugs and I had some wilt, with no signs of the beetle, so I think it was the squash borer. Anyhow........I made it through the summer and got at least some cucumbers. I made our garden a little smaller this year and moved the cattle panel arch trellis that I grow cucs up and so far, so good. So I don't know if rotating the location helps, but I doubt it. I hate killing things, but there were so many squash bugs all over them last year, I ended up going out a couple times a day and drowning them in a jar of soapy water. I just couldn't sacrifice my cucumbers for them! I grow Waltham butternut squash up my kids old swingset lined with wire fencing and they do great. Fortunately, the squash bugs don't seem to like it. A couple years ago I moved my zucchini to my back yard.......well away from the garden and I think that helped to not attract the squash bugs. They used to be the main attraction for the squash bugs in the garden.

I feel bad for you guys who are losing their cucumbers. Sorry! But do keep your eyes open for those stripped cucumber beetles.