My guess if you were in the south and the plants were in the ground would be early fusarium symptoms; but with your location and the fact they are in pots which I assume don't have soil in them then maybe it is early blight. Unless you got a plant that was already infected from a store.
Clip off the whole leaf stems with the yellow leaves and spray the plant with Daconil every week for a couple of weeks and see if it slows down or stops. If you are organic then you could try a copper spray but I have not had as much success with it and early blight.
Bill
|