Good question about the humidity...I live in an area that doesnt have that problem in late summer. Couldn't hurt to mix a little baking soda with the diluted skim milk solution. I do that for my roses in the spring when the humidity is high and they have the white type of mildew. This looks more like a fusarium wilt problem or something that is coming from stressed out roots. BTW the one year I used a tablespoon of epsom salts in the bottom of planting holes for my tomatoes was the worst year ever. They hated it.