3 gallon pots are pretty small for almost all tomato plants and most growers frown on using real dirt for container growing. If I am understanding your post correctly you mixed MG potting SOIL with your own, as in back yard SOIL? Soil in containers suffocates the roots, leading to all kinds of problems.

I know this is not about leaf spots but was the closest I could find. I have 7 week old tomatoes most about 4-5 ft. tall. I have lots of bloom.Two days ago I added Kool Bloom to them (2-45-28) Yesterday I noticed lots of new growth on the tops, the tops going all curly and winding all over.Today I notice dark spots and long black streaks on my stalks, mainly where the small stalks grow from the main stalk and on the main stalk too and the smaller stall are splitting from the main stalk.Leafs are a little soft and droopy on the tops, I'm afraid I may have O D them.I guess I'll just have to wait and see,but if anyone can give me some insight to me ,maybe before I go out and find them dead, (man that hurts to think)I could use some encouragement!!

So focused on the added Kool Bloom that I didn't mention that I also spayed them down with Sea Magic mixed with Alaska fish emulsion.The white stuff on the leaves is where I dusted them down with Viper (like Sevin dust), then that evening it rained.I never watered or put anything on them in the heat of the day. Very early morning or late afternoon.