The plant was over 6ft tall & had already produced a few cukes when I noticed a strange wilting occuring. Then the stem started to turn tan s few inches above the bottom. It was in an Earthbox with fresh medium.
When I used Google Lens it shows it could possibly be fusarium or a bacterial blight.
I see no bugs in the medium I removed today, nor have I ever seen any before. When I cut the stems there was no white oozing in fact quite dry.
The other cuke was showing signs of the same blight so when I was removing it the main stem just came right off in my hands, no cutting needed.
I have removed the EB & the medium, washed & disinfected the parts & hand shovel etc.
Any idea what it was?

Bacterial wilt is common on cucumbers, and very few are resistant to it. And this, and other diseases, are easily spread by insects. I plant County Fair, for the resistance to the wilt, and WS 58 has done fairly well the last couple of years. I spray with Surround, and some potassium bicarbonate, as a prophylactic. But eventually they seem to come down with something, carried by the bugs.

Maybe check your local extension agency, to see what diseases are in your area?

My straight eight seems to have collapsed like that and the description of bacterial wilt fits. The suyo long might be next, it seems sulky lately. Cucumbers seem to be tough to keep going for long in my plot, but this year has been better than most. I don’t do anything active to prevent disease, though.

Thanks everyone, I have never seen this before in all my 20 plus years of growing cukes. Bugs rarely bother them here, not even aphids which are all over the tomatoes & roses. If anything they get spider mites later on. I'm really bummed out about it as these Japanese hybrids are my favorite, next to tomatoes. They're about $5 to $6 a lb now @ the stores & farmer's market so I must grow them myself.
Fingers crossed my 3 other EBs with cucumbers don't get this.

I wonder if there might be some nematodes contributing to this.

@@Shule for sure nematodes might be involved in my garden when cucumbers are involved. I solarized the bed they are in last summer, but never felt it got hot enough to obliterate the nematodes.

I never looked at the lower stem or roots on my dying cucumber vines but with bacterial wilt the entire vine wilts almost all at once.

It is spread by cucumber beetles and I usually only grow the resistant variety, County Fair as recommended by @pepperhead212 .

This year I am growing another variety also because it was a pack of seeds sent to me by a friend. I forget the name but we'll see if Bacterial Wilt appears before I get more than one or two cukes like usual.