The lower older leaves of my tomatoes have these brown spots. When looking close they seem to be see-through, like the green is just gone from those parts. It looks the same on the bottom of the leaves. The veins remain green. Some leaves have just a few spots which are pale green, and others are much more effected with the large brown spots. They are in containers, and I live in North Texas. Is this a nutrient deficiency or something else? I have not fertilized as often as recommended. I haven't sprayed them with anything.