Beginner Gardening: Black spots on tomato leaves, 5 by aHtm1324

aHtm1324 wrote:
First year growing tomatoes from seed. I transplanted my seedlings 3 weeks ago in the open garden. Today I noticed these black spots on the leaves of a few plants. Is it a disease? It seems older leaves are more infected than younger ones.

I removed the infected leaves and I was wondering if I should spray with something to prevent spread of the pathogen. I only want to use organic treatment though. Any suggestions?