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Do you ever have a tomato plant that dies for seemingly no reason?
(sh.itjust.works)
Your Ultimate Gardening Guide.
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Nah usually it's my fault.
Since you tried nutrition I would suspect injury to the plant has allowed some kind of infection in. I would try trimming away all of the diseased or damaged plant matter and then applying a copper fungicide. I've had tomatoes with vines split fully in two and the plant stayed productive and vibrant once it got far enough from the damage and new growth was happening.