Are the fruits also splotchy? If so, probably cucumber mosaic virus.

Otherwise, it's probably squash bug damage. Even if you killed all the bugs (unlikely), the leaves won't heal. The plant will continue to put out new growth, though.

Just my opinion, looks like fungus. An extension agent was telling me that cucurbits like cucumbers and squash are really being hit hard by fungal diseases this summer. Looks like this one is headed for that big compost pile in the sky. Too far gone. As much as I like heirloom veggies, modern hybrids with disease resistance do have advantages!

I'm surprised people are still getting cucumbers -- I pulled mine a few weeks ago after a very productive few months.

Thank you all for responding. I think you're right about the fungus, so I pulled all the cucumbers up this morning. Going to start working on my Fall garden.

MiKru, I'm still getting a few but most of my plants were pulled out weeks ago.

I have a few cukes still on the vine, not quite ripe, but the vines themselves are just about dead.

I received good advice -- maybe on this forum? -- a few years ago, and that was to pull plants sooner rather than later. The bugs home in one dying/wilting plants, attack them, and then lay eggs in the soil for the next season.

My gauge for cucumbers is pickle worms. If the plant looks bad and I'm finding a lot pickle worms in my cucumbers, the plants gotta go.