Take one gallon of water, exactly. Add one cup (8oz) exactly of plain clorox bleach. (not store brand, not splashless, not scented, etc...plain clorox bleach. It's a formulation issue) Put this mixture into a regular pump sprayer. Spray plants entirely (affected and not affected parts) until it's dripping. From both sides and be sure to get the spray underneath the leaves and in the middle of the plant if you have it staked. Stand UPWIND! Do this AFTER SUNSET. When all the bees have gone home and the plants won't be exposed to strong sunlight for several hours. I don't bother pruning off affected parts. They will die anyway and IMHO that just spreads the blight around. They will look like hammered heck for a week or two but if the disease wasn't too bad will recover. I usually feed mine somethingorother the day after I spray them.
I came THIS close to pulling all mine this year due to blight. Copper wasn't doing a thing and I was worried about it building up in the soil. The bleach kills the blight(s) and then oxidizes within an hour or two and is gone...It's not organic but it's not something that will hang around as an endocrine disruptor.
Next year I'll be sure to plant a variety that's resistant to lots of stuff. BUT, I looooove the little drying tomatos I planted this year as they are certain to set really well even in the heat we have down here.
BTW, I’ve started spraying my roses with this stuff every 2-3 weeks. No black spots! And it’s WAY cheaper than the bought stuff for black spot. I dilute it a bit more, 6oz to a gallon.