Powdery Mildew is most often a whiteish dusting on leaves and seldom causes real problems for the affected plants. Take a sample, in a sealed plastic bag, to your local office of the University of Florida USDA Cooperative Extension Service. Here is a link that might be useful: University of Florida CES

Environmental -- sun; bright light; and/or brief water shortage.

Thanks for the feedback! I decided I didn't want to mess with them anymore so late in the season, so I just took off all my green tomatoes and brought them inside. Now I'm researching ways to ripen green tomatoes (I'm seeing newspaper is a popular method). But I will try the Sevin next year if I have the same problem. I'm going to try a non-heirloom variety next year to see if I have better luck. I did try taking a picture, but my camera is acting up and would not behave. I'm pretty sure it was the beetles. They would burrow their way inside and just eat themselves silly. Thanks!

Jean, Thank you for the notes! I agree about their size. :( I didn't realize how puny they were until I saw my friend's cucumber plants which she planted only about a month ago. But she is already in the middle of her second harvest, when we have only had one (fruitless) flowering! Below is a picture of how they normally look. 2/5 plants are affected by these issues. We didn't do very much to the soil before planting. It was mostly clay when we installed the raised bed boards, so we dug it out a few inches to get more depth. The garden bed is probably about 6" deep from the top soil down to where we dug it out to the hard clay-like soil underneath. They were seeded, in late February / early March. I don't know the exact seed date. We are in Houston, TX at hardiness zone 8b/9a. The soil mix we used was store-bought raised-bed garden mix, from Miracle-Gro's Nature Care line (link). We filled initially with that, and the topped it off with potting mix of the same brand, sprinkling as needed when the soil settled and/or roots became exposed. We haven't fertilized at all, except for putting in some of these fertilizer sticks when they were younger and we still had them lying on the ground. Again, thank you for the advice!