When the soil becomes waterlogged from too much rain, irrigation, etc., the roots can't take up any oxygen, or nutrients and so tomato plants will turn yellow and wilt.

If there's any standing water try to dig wee ditches to get the water out of there.

The normal sequence is foliage turning yellow and wilting and the foliage turning brown and when it's all brown the plant usually doesn't make it.

So do hope that conditions change and the soil has a chance to dry out. Adding fertilizer isn't going to help b'c the roots can't take it up and applying it to the foliage directly isn't going to help either b'c the main problem is lack of oxygen uptake through the roots.

Carolyn, who has been through this many times when she was growing several hundreds of plants in a field and there were a few low spots that would fill up with standing water that she tried so hard to drain. Another observation is that some varieties do better and last longer under such conditions than others. So fingers crossed.