Agree it doesn’t look like septoria. It looks purple — is it? If so, it could be phosphorus deficiency. Blossom end rot is caused by a calcium deficiency that can be aggrevated by watering inconsistencies.

My tomato plants lost nearly all their leaves halfway down from something fungal and they’ve still produced tons of tomaotes. I just remove the diseased leaves whenever I see them. I always water at the base of my plants but there’s just been too much rain this year, spreading the fungus around. I grow Early Girl, Better Boy, and Beefsteak.

@Labradors @party_music50 @lovemycorgi z5b SE michigan thank you for your thoughts I appreciate it! I'll remove the leaves! The plants are still producing a lot, which is great.

This fungus in endemic in your bed, so you might think about strategies for future years. Removal and disposal of infected leaves will help prevent its spread. Fungicides should be applied proactively. They don't destroy the fungus once it has been established. As in, don't wait until you see the damage. Rotation among several fungicides is the best bet, since resistant varieties soon get established.

It’s key to remove affected leaves from the garden entirely - throw them away or burn them - do not compost them.

Water splashing dirt onto the leaves also spreads fungal disease. So does water splashing from infected leaves to other leaves.

You can’t prevent rain, but you can avoid overhead watering (use drip irrigation or water gently at the base of the plant to avoid splashing). Use mulch under the plants So dirt doesn’t splash on them when it rains.

Rotate crops (don’t plant nightshade family plants in the same spot for three years).

And yes, you may have to use fungicides.