I showed it at my local garden center, but they said its normal for old leaves. But I think its some disease, as the new growth also gets similar blackening of leaves within weeks. This only happens to leaves that are in touch with other infected leaves. Need help identifying what is the name of this disease and what are the remedies, if any.
EDIT: Adding many pics, the one that shows totally brown plant, is the one which the original image was from. All other images are from another plant which also has the same disease, but I'm making it survive by regular removal of diseased leaves.
To answer @stormy's questions: - watering practice: 1gallon every 3rd day - soil: I just potted the plants in my backyard's garden soil(which is a little clay-ey). This is in california, zone 10a - fertilizers: i just added the fertilizer once while transplanting the seedlings - epsom salt: I only used it once - tomatoes never became black, as you can see in the pic(even on the totally decimated plant, they were fine)
It was gradual blackening, and i'm very sure it was not in a matter of days. One thing that could have contributed to this was that I never did any pruning before the offset of the issue. I used a 42 inch cage, but the plant was about 4 feet long, and started bending. It became very heavy, so the cage was not sufficient, and I had to use wooden sticks and wool to make it not fall on the ground. Anyways, the gist is, not much air circulation probably.
The original picture that I shared was about a month old, so out of 4 plants, 2 have totally dried out. The remaining 2, I keep pruning leaves which show symptoms of unhealthy leaves, this has helped in reviving the plant, though it is not fully free of the disease.
I'd like to know if this still looks late blight to you, it actually started around August first week I think.