Wow, this place is nothing w/o Carolyn posting

Ouch. Looks nasty.

How fast has it been progressing since you noticed it? Late Blight can kill a tomato in a week, and while I'm not seeing the trademark black "slime" it makes of dead leaves, the broad swaths of dead leaf with no obvious pattern suggests a fast-moving fungus to me. If air circulation weren't so good I'd be guessing grey mold.

If it's getting rapidly worse, pull the whole plant as soon as humanly possible, bag it up, and dispose of it in the trash. Whatever happens, I'd start hitting any tomatoes and their relatives (potatoes and peppers) with Daconil... it's almost harmless to people, and with something that looks this close to fungal in nature it may help your other plants survive.

If it hasn't changed much, if at all, in the last four days, pick off all of the affected leaves and start applying Daconil. This problem is not bacterial, not an obvious root problem, and doesn't strike me as viral, so treat it like a fungus and see what it does.

Good luck.

--Alison

Thanks for the response Alison,

I actually must have gotten very lucky. I butchered that plant so only clean leaves were remaining and cut some stuff off one next to it that looked iffy.

I then sprayed the hell out of them w/ Daconil.

Seemed to have worked, thank goodness.

Well, there's something to be said for drastic measures... I hope that's solved it.

Best of luck for a smooth season from here on out.

--Alison