Also: Would I still be able to get a good crop if I replanted at this point? I'm in zone 8A where summer lasts well into September.

I find it confusing, because to my untrained eye a lot of the problems that can plague cucumbers look a lot alike. I am having a similar problem, and I hate to break it to you, but it looks like downy mildew. I am not getting the impression that fungicide treatment will be effective.
My cuke pics at:
http://www.flickr.com/photos/8698937@N02/7698912572/
http://www.flickr.com/photos/8698937@N02/7698870098/
The sad thing is, I was doing everything right--trellis, mulch, not watering the leaves--and they were looking better this year than ever before, plus few cucumber beetles. I have not had one fruit, and I'm probably going to have to pull them!

In zone 8, you should be able to get a second crop, just check the number of days to maturity on your seed packet and calculate the days until your first frost--plus leave wiggle room for the shorter days. hope that helps

Mine were doing great til about the 3rd wk of July and now look exactly like that! I keep wanting to replant them too! I might see if I can find something tomorrow at a nursery and replant them this wkend. I was really enjoying lots of cukes for quite a while. Maybe it was this bad summer of too many heat waves! Don't know! But I think I'm going to give it a try to replant! Best of luck to you too! I'd replant and you could even do them in a moe controlled container kind of thing where you could cover w/ a cold frame!

It is fungus look t the white spots on the leaves. I had the same problem. I sprayed and sprayed. Some of the plants especially the squash recovered. You are lucky your plants still alive I have guys who suck the juice from the stem at the soil level and the plant dies. Some one told me to use one part peroxide and four parts water and drench the soil at the root to kill these lava or whatever i did the jury still in session.

You should check with your local cooperative extension or master gardeners. In my city, they set up a booth at the farmers' market (or ask someone at a garden center)--that is the only way you are going to get a real answer and solution that may work.

Hi Jessica, I like your trellis, but sorry I don't have a diagnosis. It sounds that the plant was producing delicious cucumbers for a while, right? I, too, was very frustrated with mine because they always produced well but never long enough. Through help from this forum I adapted some changes this year and so far I've been getting great cucumbers everyday since mid May. To extend the harvest I made the following changes:
1. Never use up all garden space at the first spring planting. I reserved some space for successive planting.
2. Pick cucumbers when they are young and pick daily so the plant doesn't "age" as fast. Aged plants are more vulnerable to diseases.
3. Repeat planting about every 4 weeks. My second planting is at it's peak right now, and the third planting is almost ready to fruit. I've found that 3 plants at each planting is more than enough to supply for a small family.
We're blessed with a long season in southern California; maybe that's why the above changes worked well. I hope you'll continue to get delicious cucumbers.