If I saw that on my tomatoes I'd say "Early Blight". And then I'd chop off all the bad leaves and get them out of the growing area. Sanitation pruning accomplishes two things:
1) Take away spores to reduce spread of the whatever, and
2) Improve air circulation to reduce damp areas where spores germinate
IMO this has to be done whether you spray or not, and no matter what disease/pest/deficiency is involved. Leaves in the process of rotting are full of micro-organisms you do not want handy to your plants. Ruthless pruning is required.
If this is only on the lower leaves, I would suggest feeding the plants as well.
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