Could it be CMV? Link to photo below...

Here is a link that might be useful: {{gwi:45087}}

I am continuing my search and think maybe it could be: Anthracnose, caused by the fungus Colletotrichum lagenarium, is a severe disease that spreads rapidly in warm, wet weather.

Not a disease.

I think it ran low of water, even though that may have been only briefly. Most likely during a hot spell which caused rapid drying of the leaf between the veins.

The damage in the photos below occurred in the space of ONE day! I was shocked when I found it, and looked under the leaves to find a single cucumber beetle, which I promptly squished. Funnily enough, there hasn't been any further damage, as I've hunted the boogers down relentlessly. I only found a few of them, but in my area it's a known fact that by August I won't be able to keep up with them.

{{gwi:92864}}

{{gwi:92865}}

I have similar problems with my greenhouse grown cukes. One year I did call Extension Service and was told to feed with two things. One I'm pretty sure was bone meal. Whatever combo it was worked. I have never been able to remember the other and when I called Ext. Serv. again no one knew what to tell me. And of course, I couldn't remember who I talked to. (There is no Ext. Serv. where I live, so I've never gotten acquainted!) I would surely like to find out what that other thing was!

lelia,

Cucumber beetles didn't do that. They make small raggedy holes.

Environmental stress is *much* more likely.