To me it looks like the leaves got wet and got sunburned. It doesn't look like a bug or a disease to me. I would just ignore them and try not to get the leaves wet when you water.

It appears to be getting worse. Here is the problem less than a week later. It appears to be spreading to an adjacent bed.

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I ended up cutting some of the worst leaves off to prevent spreading to my second raised bed but now it seems like all of my cukes are goners.

I did end up picking two nice Marketmores yesterday but I feel like my cuke season is dissappointingly wrapping up without any answers....

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I am getting similar damage on my cucumber leaves and I'm seeing way more cucumber beetles than usual, picking them daily. Not sure if the beetle is the cause but they are often found on the underside of the damaged leaves. Check your plants for this pest especially on the damaged leaves.

Looks very much to me like you have Striped Cucumber Beetle. They feed on top of the leaves by burying their faces into the leaf surface. I had never seen them before this year when I had a surprise infestation. Check your plants in the morning sunshine. These beetles feed and mate during the day, out in the open where it is easy to locate and destroy them. Also check the cuke blossoms during the day as the beetles love to hang out in there. I was able to completely remove the infestation by relentless search and destroy missions. This may not be your answer but I think it's worth checking for sure.

I always plant three or four generations of cukes in order to beat this kind of stuff.

I don't know if it's a winning or losing battle but I am picking 20 -25 beetles per day, I wonder how many I need to eliminate before I start seeing a difference in their numbers.

Rich, which type of beetle are you picking? I was definitely successful with picking Striped Cucumber Beetle. But this was my first year with them and they weren't that well established. I would still think in two or three years you could beat them back to very low numbers.

I'm picking the striped beetle and plan to do so several times a day whether I see a noticeable reduction or not. As I said earlier I'm seeing far more than I normally do, today I got five in one male squash flower. I have about 12 good looking cucumber plants but I'm concerned that with all of these beetles it's only time before disease sets in.

Wow, I'm real sorry about your cuc plants. I never had much luck with cucs. However, your plants don't look like goners just yet. I would recommend using Diatomaceous Earth which you can pick up relatively cheaply. It is pretty effective on keeping the beetles away. Just encircle each plant like a mote with the white powder. Also try using insecticidal soap or you can make a solution with dish soap and water and spray the leaves. It looks like something splashed up from the soil and infected your plants' leaves - spores or something. Try putting down some mulch to make a barrier, plastic or 4 inches of straw or grass clippings work well.

per dogwood I dusted the plants perimeter with Diatomaceous Earth last evening, and today I have only found two stripped beetles SO FAR. It's a cloudy cool day so not sure if that plays a role but so far so good.

I have the exact same thing - it's a fungal disease, probably Angular Leaf Spot. I have done nothing because the rain is incessant and very heavy. I don't have the resources or desire to spray fungicide several times a day (it has been raining that much). I remove the worst leaves and trellis what vines I can. Still getting fruit and new growth, for now.
Angular Leaf Spot (bacterium - Pseudomonas syringae pv. lacrymans): This disease appears on leaves, stems and fruit. Spots are small, angular, straw-colored and watersoaked. Leaf spots often dry and fall out giving the leaf a âÂÂshot-holeâ appearance, similar to those caused by anthracnose. Spots on fruit are usually smaller and circular in shape. Bacteria overwinter in crop residue and on seed. Hard rains splash the bacteria to stems and leaves. The disease may reach epidemic proportions during periods of heavy rains, particularly if temperatures remain high. Crop rotation with non-cucurbit crops is helpful for control of angular leaf spot. Application of copper fungicide will assist in control. Cucurbits, however, are sensitive to copper when young, and repeated applications of copper may cause yellowing of foliage around the edges of the leaves.

Here is a link that might be useful: Texas Plant Disease Handbook

It might be angular leaf spot but mine are actually holes so I'm not certain its the same thing. I have been checking for beetles morning, day, and night and see none.

As I am get new growth, I trim off the worst leaves daily. The new growth seems to be unaffected. I wonder if it has anything to do with the slime mold that formed on my beds at the start of July. I covered my beds with Long Island garden mulch and it literally formed a solid surface on my beds. I removed it as soon as I noticed it and have since covered the beds with fresh compost.

I'm pretty sure once again I'm going to be disappointed with a shortened bounty after a great start. This is frustrating for me because at my old house (5 miles away) I used to have so many cukes that I couldn't even give them all away. Tomatoes too.