That's early blight. No reliable genetic resistance is available. About this time of year, I prune off all the lower leaves that have lesions to reduce inoculum. The damage will stop 2 feet or so up the plant, where the leaves stay dry. Here is a link that might be useful: Pruning for Early Blight

I'm going by the spot on the leaf in the first picture just right of center and the leaf on top just left of center in the last picture. You may also have a deficiency or herbicide problem. Has anyone there sprayed roundup lately?

I am not a expert on disease,but I had a similar problem a few weeks back. Here is the thread on my problem. http://forums.gardenweb.com/discussions/3035569/kind-of-scary-looking-disease?n=11 Once I removed the damaged leaves it has not returned. Hope you get an answer.

Do you take mulitvitamin/multimineral supplements such as One A Day or Centrum Nallah? The minerals used in these two and nearly all supplements are chemically created minerals produced by humans and the exact same minerals used in so called non organic fertilizers for plants. Such as potassium chloride, magnesium oxide, dibasic calcium phosphate and many more. We use the same elemental elements as plants do. and extract them only in their pure form known as chemical elements found in the periodic table of elements, if you remember high school science. Chemically created synthetic fertilizers are simply a combination of two or more organic elements, sometimes using high heat, to extract the pure chemical element plants can take in, along with humans. We can't eat phosphate rock or limestone but we can extract the elements of phosphorus and calcium we can consume, same for plants. Soda drink has phosphoric acid in it along with tooth paste, Phosphoric acid comes from treating organic phosphate containing material with sulfuric acid, Sulfuric acid is a natural organic salt of sulfur and also organic. So where is the danger? The idea that man made chemical fertilizers are dangerous is a myth and this is where the danger is. I say a dangerous myth because without man made synthesized fertilizers over half to three quarters of the world population would starve. Not may but would without a doubt. People who think only organic is fine only if they know the facts and not try to force everyone to do the same. it would take 30 tons of cow manure to fertilize 1 acre of crop land to produce half the yield they do now. 30 tons of cow poo requires about 4 cows. 4 cows require 8 acres of good forage land per year. Removing the manure to fertilize your crop land would then reduce the forage available next year. The next year even less, and so on until your 4 cows starve. If you did the same with alfalfa each year the source land would become depleted, and any organic source would quickly become depleted. The world would starve, and organic vs chemica is a major rant of mine because people don't know how sensitive the world food supply is and could easily collapse with the wrong laws by the wrong people. 2,7 billion acres are used to feed the world population and people are starving now, this doesn't include land used for livestock. 2.7 billion acres would require manure from 11 billion cows to support the land by ORGANIC means, but wouldn't last long. You can use organic fertilizers as a personal choice but please be aware most of the worlds population would die without man made synthetic fertilizers made from natural elements that are perfectly safe.