What's causing my tomato leaves to look like this? They have brown or black spot on them, the leaves start to yellow, then they brown and eventually die. I don't see any visible bugs. I live in Florida if that makes a difference.

Julie, please fill in your personal profile so that your location will appear in all your posts. See mine in the upper right corner.

Here in FL we have all sorts of diseases and blights that get your tomatoes at this time of year. They generally don't live through June here, anyway because of the hot nights. Even if they do survive, most tomatoes will not set fruit once the night temperatures go higher than 75 or so. Best tomato growing here is in the fall - plant in September and you can keep the plants producing through winter with just a sheet of frost cloth to protect for cold nights.

I would think you've got either fusarium wilt or a late blight (which is a virus) going on there. You can try dousing the root system with a weak solution of hydrogen peroxide (get some 3% peroxide at the drugstore, dilute 32/1) It may carry your tomatoes through until at least you can harvest some. But no guarantees.