It may just be there time to go . . . the leaves, not the tomatoes. If your growth is vigorous and you are setting fruit, I wouldn't freak out just yet. Tomatoes will show signs of planting stress sometimes especially on leaves that they already have at the time of planting. If the leaves become too damaged, or unsightly, or just yellow out completely, just take a sharp pair of scissors in the late afternoon and prune them away (I use bonsai shears.) I like to prune away everything that grows 10" or less from the ground anyway to discourage disease and encourage airflow. Getting enough air shouldn't be a problem for you, though because you look like you've got plenty of space. You look like you know what you're doing, you've got plenty of space in the row, you've got fruit growing, you look like you've got a good mulch going, bravo! You might want to take a sturdy wood stake and push it into the ground beside that cage. You can tie the cage to the stake. I recently suffered a lot of wind and storm damage to my tomato garden because my cages did not stay anchored in the ground. If you are still worried about fungus, I'd get a spray that is organically derived, or advertises being gentle on plants and give her a good spray. I am not an expert (far from it as my posting prove), but I'd think a disease would cause the plant to show more of a sign all-over. Tomatoes like to keep growing and sometimes they'll stop taking care of old leaves in favor of new growth. If you get pale or yellow new growth, try a dose of epsom salts and wait a few days and see if there is a change. Remember to use more because your plants are in the ground and water the salts in well.

Early blight and Septoria leaf spot both have a tendency to hit the older leaves that are closer to the ground first. To be safe, I would remove the affected foliage and get some sort of anti-fungal spray to prevent it from jumping to other tomato plants or foliage. I think that there are both organic (copper and sulphur) and non-organic (Seranade, Daconil, etc.) sprays available.

i would put sevens dust on e'm to keep the bugs away so you don't get holes in your leaves!!!.....