Answer: It is difficult to diagnose a plant problem without seeing it. Yellowing leaves can indicate overwatering or a nitrogen deficiency and spotting can indicate a fungal or bacterial disease. I can't really tell without inspecting the plant. Crop rotation is important to guard against soil borne pathogens but growing the most disease resistant tomato varieties will also help. I wish I could suggest some control measures but I just don't know what might be causing the problem. Sorry I can't be of more help.
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