Look at the base of the main stem to see if there is any orange-yellowish gunk there. If there is, your cucumber has fallen victim to the dreaded squash vine borer, which can also attack cukes. The worms bore into the stem of the plant, which causes sudden wilt and eventual death. You'll have to pull the plants and throw them away, unfortunately.
If you don't see any evidence of the orangish "frass", you may just be watering too much. Has this affected all of your cukes at the same time?
I also have this problem and thought it might be cucumber wilt caused by the cucumber beetle. I haven't seen any beetles in the garden, though. Is there any preventitive measures that can be taken, if is the vine borer? We have this problem with the cucumbers every year, sometime affecting just a few of the plants. Suggestions would be appreciated.
Unfortunately, the vine borer is extremely destructive and is usually caught too late. At least with squash, you can sometimes slit open the plant stem and remove the worm - cucumber stems are just too narrow for that.
The best thing you can do is cover your plants with a lightweight cloth to prevent insects from getting at them. Of course, the problem with this method is that the flowers may not be properly pollinated by bees, so you'll need to remove the cover every once in awhile.
Thanks for the tip of using catnip as another companion plant. that grows wild here. I'll just let it grow instead of getting out the hoe. :>)
I've been wondering if growing that ghost pepper and making an infusion to spray around squash and cukes. It might make them a little confused as to weather their favored vine is even there, could be worth a shot. LOL
As for DE, it's certainly worth a try. You would have to cover the plant's stem with it. The eggs are laid on the underside of the leaves by the SVB moth. Then the larvae crawl down to the stem where it meets the soil and bores in.
Some folks have found wrapping the stem with pantyhose seems to work. I don't think this would be a good remedy for cukes, though, as the stem is so thin.