PepperJane,
I sympathize with you, it can be frustrating, but not all foliage diseases are blight and not all blights are the same. Some nightshade diseases are inevitable as the weather changes for the worse and will eventually kill them. My tomato
plants are oh so unhappy right now. The low last night was 4C and my
plants are over 8' tall, so it's not really practical to try to cover them so they were forced to fend for themselves. We have 2 tomatillo
plants in pots that we took indoors, though. My tomato
plants all have some sort of foliage disease on them right now and it's only a matter of time before they croak. Any fruit that looks remotely like it's trying to blush and ripen is picked and left to ripen on the table. Probably in the next couple of weeks, I'll go out there and rip out the vines, hanging them upside down in the house to let the remainder of the fruit try to ripen as best it can.
Bottom line, even with blights and other diseases, you can still get a bountiful harvest if you prepare your soil in
spring and Fall diligently with plenty of compost, feed after transplanting and again at fruit set, and monitor for insect pests.
Buona fortuna and wish I could offer more consolation,
Julianna