Look up late blight of tomato and see if it fits.

Fungal. Looks like Septoria Leaf Spot. It's happening to me right now, and usually happens about fruiting time. If you catch it early, remove affected foliage, and spray throughly with Daconil. You might save the plant(s), but you have to act fast. In my case the whole plant has it top to bottom, but oddly, mostly on the backside away from the sun.

Here's mine:

http://www.tomatoville.com/showthread.php?t=47451

Allison, maybe I missed it but where are you located? With out that information, any responses are not worth much. What mix are you using in the pots, how do you determine when to water and/or fertilize, plus much more information. If you aren't confused...you should be. Maybe I am the one confused. LOL

I don't think soil mix, watering, or fertilization is an issue here. The plants pictured here are loaded with fruit. They WERE healthy.

Thank you, this is all extremely helpful!! I think it looked the most like early blight, but knowing it was fungal is enough to go on for prevention this year. I think I'm going to start over with new mix, clean the pots with bleach, and start using Daconil early. The bamboo stakes were outside all winter but seem like they would be hard to disinfect- should I just get rid of those?

Oops, thought my location was on here! Boston, MA- though these pictures are from mid-late August last summer.

They were short of water. 5-1-1 drains exceedingly weel. Lots of plant in a pot need frequent irrigation.

Yellowing may be due to nitrogen washed out of pot with irrigations -- common in containers.

Yeah, that looks more like drought stress to me as well.

You might want to take your pictures to your nearest USDA Cooperative Extension branch office and see what they suggest.

How quickly did your plants die?

Sorry for my absence- way too busy this year. Wow, drought stress does look a lot like it. I guess I went too far in the opposite direction with drainage... now that I think about it, it got worse after I was away and relying on a drip hose on a timer for a little while, too.

They died relatively slowly- I don't think I actually pulled them out until October, at which point they looked extremely sad but still weren't 100% dead.

I was going to just use new bagged potting mix this year, mostly due to time but also to keep things from drying out too much (mostly using fabric pots now), but after planting half my transplants it's alarming how compacted it looks. I think mixing it evenly with pink bark mulch should give me roughly 5-1-1-ish proportions, and then I'll just keep a closer eye on the watering?

The fact that your plants were loaded with fruit doesn't sound much like drought stress, unless you stopped watering them suddenly. Those plants were pretty happy.

"Drought stress" = stress from lack of water that could be transient. It doesn't have to mean actual extended drought conditions. If I'm late watering my plants and they wilt, they'll show signs of the stress in brown and yellow spots on the leaves a couple of days afterward, even though the plant largely recovers. It won't have been long enough to affect fruit, but the foliage will suffer.