Answer: There are a number of reasons for tomato leaves to turn yellow but if the problem is spreading, I suspect it is a fungal disease. Disease are difficult to stop once they take hold of a tomato plant. You can try an application of a fungicide to see if that will help. If the disease is only on the leaves and not throughout the vascular system, it may be that a fungicide will help control the problem. I don't think the bugs in the soil are causing the yellowing leaves. I hope your plants recover.
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