I have big beautiful tomatoes that are slowly going to pot. Many of the branches are now about an inch long and then immediately narrow to a strand and the leaves and branch beyond the narrow are completely brown and dead. Can anyone help me identify the problem so I can try to correct it?

Probably one of the 100's it seems like disease pressures we're under right now. If you're not over watering. Roll with a couple fungicides like daconil, bonnie copper. or Bonide Mancozeb or Serenade. You don't have a lot of options. I'd probably go Dac and copper. They aren't systemic. So you need to apply them every 10 days or so. Follow the labels. It's Texas and humid and hot. Disease pressure is high.

Yep same thing going on with mine

Was the stem originally " soft " right around the dirt level --before it totally died ? That kinda looks like root fungus . I had something similar last year with my potatoes , On potatoes it's called phytopthra ( sp?) . I used a microbe and beneficial fungicide to stop it from going to my other plants .

It is tomato disease. We've had a lot of rain this year, which really speeds up the disease process if you don't do something to protect them. I use liquid copper fungicide for my tomato and cucumber plants, and it helps out a lot! It won't completely prevent the disease, but deters it enough to keep the plants still alive. Also, make sure you are watering at the base of the plants. The less the leaves get wet, the better. Here is a link to the liquid copper fungicide that I use. Good luck to you next year! Also, you can try and grow more disease resistant tomato varieties. Some don't taste quite as good as the heirlooms, but to me it's definitely worth not having a dead tomato plant by the start of August. I recommend Celebrity. I grow some every year.

https://www.amazon.com/Southern-Ag-...&hvtargid=pla-348922396442&psc=1