Hi John - Yellowing of the leaves is almost always a sign of over-watering and best as I can tell from your small photo that would be my guess - too much water.. If you have been having excessive amounts of rain lately there isn't much you can do about it. But if you think you might have been over-watering, then cut your watering in half and you should see a substantial improvement in your plants. A side dressing with a low nitrogen fertilizer will help them perk up once they have had a chance to dry up a bit. As a general rule of thumb, tomatoes need no more than 1 to 1 1/2 inches of water a week as long as the temps are in a normal range.

Next year plan to use a heavy mulch around the base of your plants and then you can cut your watering even more.

No naked dirt allowed in the garden. ;)

Dave