Hi,

I had the same problem and yes it will spread to the whole plant and all your tomatoes. It's a Fungus, and it will kill you plants very fast. Thanks to Sharon Love Joy's book Trowel & Error, I found a recipe for diluted milk that saved my plants. I used a 3:1 solution(3 parts water, 1 part milk). First I trimmed off all the affected leaves/branches ( this will make your tomatoes look like scarecrows, but it's the only way)-Dont compost the diseased foliage.
Then spray with diluted milk for several days. I do it in the shade but early enough that the plants have time to dry before evening coolness sets in.

My plants are saved! I cant believe it worked!

BTW I live in coastal (June Gloom) CA, in case you were wondering about the plants locale.

Hope it works for you,

Ziggy

Well, it seems that ziggy has the same answer for every leaf spot issue in this forum.

Beyond that, you most likely have flea beetles. They're very small (less than a 1/4 inch) and jump if you try to touch them.

They may be gone or they may still be present. So, investigate before you spray anything.

Just trying to be helpful. I like to pass along things that I find helpful.
You don't have to take my advice. But don't be nasty, that's uncalled for.
Ziggy

jean001-
I did find some small dark bugs that were shaped like a grain of rice but smaller, and they did jump when I reached toward them. What treatment should I try?