Hi,

It is difficult to diagnose problems like these. It's unusual for the same fungus or virus to infect different varieties of plants. Both cucumbers and squash are members of the cucurbit family, so it would make sense for them both to be infected, but it shouldn't necessarily effect the beans. I'm wondering if these plants are suffering from sunscald. If so, you might want to build a little screen for them and keep them watered consistently. Here is some info about sunscald in a number of different plants that might be helpful:http://www.missouribotanicalgarden.org/gardens-gardening/your-garden/help-for-the-home-gardener/advi...

I could be wrong, of course, and this might be viral or fungal. I suggest taking a wait and see attitude.