Richard, sorry to hear of your garden trials and wish you lived closer for I have so many, i am just letting them rot. Was a good year around here for not only me, but others as well. hard to even give away tomatoes right now. Same with green beans, could give you several bushel if you could pick them.
On your blight problem, if indeed it is blight, then I would not worry about your soil, for early and late blight are wind blown diseases and usually play havoc in humid climates. I have been hit by both this year but many varieties weather the storm better then others. Here the heat has finally been turned on and it is taking a tole, but yet a great year.
Rotating crops is the best disease prevention you can take. I never grow nightshades in the same place consecutive. Will get disease most every time. Copper spray is said to help, but have never tried it and there might be a few other remedies out there. Hope things get to looking better for you, Mark.