In Zone 5. The variety is Mountain Fresh tomatoes which are mulched and watered via a drip system for what it's worth.
The plants have been getting progressively worse looking. I recently pruned/disposed of the affected areas as well as pruning back any branches heading towards other plants in the hopes to let the current large fruit ripen.
I'm still working on my tomato disease ID skills but based on your picture your leaf looks like it has early blight. Here is a stack exchange answer that gives great info on early vs. late blight. Early blight usually presents bulls-eye rings with a yellowing around each lesion. Late blight looks like patches of brown leaves sometimes with visible fuzzy growth.
The main difference from a tomato growing perspective is that early blight you can control somewhat and even have a successful tomato harvest. Early blight does not affect the tomato itself but will damage leaves, flowers, and stems. Late blight, on the other hand, will cause rot spots on the tomatoes themselves and can quickly kill the entire plant.
The advice for early blight is to remove all infected leaves and then create a baking soda spray which you spray on the top and bottom of leaves until dripping once per week. The solution creates an alkaline environment which is the wrong pH for the fungus to survive. It's even better if you use this before blight begins.
3 Tbsp baking soda
1 Gallon water
1 Tbsp vegetable oil to help the spray stick
2 drops dish soap to emulsify all ingredients
For late blight you can also try to control with baking soda spray, but because it affects the tomatoes and can quickly kill the whole plant, removal is advisable. Crop rotation can help so that spores don't build up in the soil. Remember, don't add any infected leaves to your compost bin because spores can remain and infect plants again the following year.
I'm currently growing about 20 tomato plants in a community garden where I have no real control over soil diseases. Everyone in the garden has blight, and I'm pretty sure I have both early and late. My tomatoes are still growing vigorously and producing more tomatoes than I can eat. I don't plan on removing until they stop producing tomatoes. Next year I'll start spraying with baking soda from week 1 instead of waiting for blight to develop. Even so I expect I will get blight again. I say this to demonstrate that although living with blight is not ideal I don't believe you need to pull out all your plants right away.
