It looks like Late Blight to me and it's a killer. Plants die shortly after you discover that they are infected and once they are infected, there is no cure.
Late Blight is carried by the wind and lands on your plants so it usually starts at the top of the plants. Early blight usually starts on the bottom leaves and moves much more slowly. I have never had a plant die of EB but several years ago I had my entire crop wiped out by LB.
I spray Actinovate starting in Late July as a preventative. some people say that this does not work but I think that it helps. If I would happen to see a plant infected with LB , I would immediately pull it out because there is no hope it will survive and spray the rest of them with copper.
LB arrives here in August when days are humid and nights are cool. When the nights are still hot like in July LB is not an issue.
I get my tomatoes started early enough that if LB gets them in August, it's still sad but at least by then I have already had a decent harvest.
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