Most of my tomato plants are doing really well. But the one in the cage highlighted in red started failing a few weeks ago. I fertilized with some Miracle grow I had lying around and it didn't improve. Then I got some Tomato Tone. That did nothing. The plant kept getting worse and worse and now it's just a husk. I'm afraid blue is following next and I'm concerned about purple. Here's another angle for some more context. .

Any thoughts?