Give up. If they are dying, throw in the garbage not your compost. But maybe someone else on here won't be as negative as me.
It would help with some pics but I'd start again with new plants. Also it would help if you told us how you are growing them.
If it is Phytophthora, you need to lift the plants and get rid of them. Be very careful the remains. Bag them or burn them.
First lets see what they look like ! Overwatering can also be a possibility ! Does the discoloration extend to the branches ? If not you can cut a few of them and root them in water for new starts ! How is the weather where you are ?
I sure would like to see some pics of your tom plants. Mart is right—first see, then discuss the possibilities.
Anna, Mart has a good idea about rooting some healthy cuttings & starting over. Do you have enough time in your growing season to do that? Oh, wait, I just saw you are in New York. No, you don't. But there is next year. Mart's suggestion is good advice that I will try to remember. Tomatoes root very easily. Frankly, I have always had the best luck with self sowed tomatoes. Meaning volunteers that I didn't plant. They come up later but are much more disease free and produce more tomatoes. ?? Not sure why. This year a yellow tomato showed up that has been a great producer. I haven't planted any yellow tomatoes so I have no idea where it came from. So, have any of your tomatoes ripened? If so, let some of the seeds stay in the ground for self-sown volunteers next year. I wish you good luck.
