Yes, I would cut and begin copper spray if not doing already. I get the same over here in NY and now find it better to be a little more preemptive. I trim the lower leaves so nothing hangs below 12-18" from the ground, and start spraying with the copper fungicide in June. When I had it in the past it would at least travel slowly up the vine so I would still get a lot of top growth and tomatoes.

Actually looks more like Septoria leaf Spot to me but it really makes no difference as the treatment is the same. But "poisoning the bed" isn't really a valid concern as the spores are air borne. The only way to avoid them is to grow in a vacuum.

Do keep in mind that there are many different copper-based fungicides, not all of the same quality, and there are non-copper based ones that have proven to be more effective at control.

Dave

Definitely remove it, but I'm not sure it's blight. Is only one branch affected?