I just recently got hit by the powdery milder thing on my zuke plants and some of my pumpkin, as well! Seems like the mid summer humidity brings it on big time! I ended up cutting off all affected leaves and would have just taken out the entire plants were it not for the discovery of some healthy lookng green leaves. Gotta keep an eye on it, however. I do use fungicide spray and it doesn't help that much if it's already affected. I will spray some fungicide spray on the leaves after tomorrow's storms get thru.
I like your caged area. You must have a lot of rabbits in your yard/neighborhood. We do too and have to fence in everything, even the herbs!
Good luck! Might be time to pull a lot of it out and start on your fall stuff! You might be able to still find some already growing tomato plants at a local nursery and stick them in the ground now or in a large container. I sometimes see tomato plants at nurseries this time of the yr that even have tomatoes growing nicely on them!!! Do you use any sort of fertilizers?

will cutting off the affected leaves hurt the harvest in any way? and where do you cut them?

i didn't fertilize until a couple of days ago...well actually i added top-dressed the soil (from my tumbler) about a month after planting (it was a combination of grass, fruit/veggie scraps, coffee beans, and a small amount of firewood ash). i noticed that dye to the dry spell, the compost literally petritified itself.