The late summer diseases on tomatoes go crazy this time of year… septoria leaf spot, blights, anthracnose. At least in my muggy hot weather, it can run rampant! The best defense I know is to cut it all out and burn it. These tomato diseases are caused from fungal spores and bacterial that travel through the air and love humid conditions. Its quite normal, at least in my region, and I battle it every year. You can try a commercial copper spray or make your own, but mine usually progress too fast