Could you show a pic or two and give your location/zone/climate?
Also tell about fertilizer, water, mulch, sun, compost, beds, ripeness and so on? There are a LOT of things that could be wrong, and that info can help some of the people here zero in on the more likely possibilities.

I live in Modesto, right in the heart of the central valley of CA..It is hot here and very dry. I water the 3 times a week allowed long and slow. It is my private time. When we have several 100 deg. days I will sneak in another .watering.I use a 12-5-7 with coffee grounds and egg shells. There were 5 plants and 3 cucumber plants in a 4x12 bed. The cucs died
within a week of their leaves wilting and then the tomatoes. I have 4-5 in of redwood compost in the bed. The plants were lush and they tasted really good and this just started 2 weeks ago. I didn't live here last summer but I grew chard and flowers last winter. Thanks for your help.

I have experienced similar issues in the past couple years (live in central PA). Your cucumber problem sounds like bacterial wilt caused by bacteria deposited by cucumber fly in early summer. I lost whole cuc crop a few years in row. Finally started spraying with Sevn couple times after June 25.
See my post following this with my tomato pics. Looks similar. I get small black spots before they turn yellow then curl up and die - mid-season after bearing soem decent fruit.