So here am a second year gardener, making few of the mistakes I made the first year. I'm growing mostly heirloom tomatoes from seed. Last year nearly every seed I started died a leggy death. I'm doing mounded beds and containers all in my small backyard. Everything was going great! OK there were a few set backs, but on the whole my garden looked fantastic and my toms grew bigger daily and all are setting fruit.
Then I noticed my beautiful Crepe Myrtle (that's a tree) had some whitish powder on some of the new leaves and I thought maybe that's the way they come out and wasn't worried at first but I kept checking those leaves were curling and dying! I got out my Actinovate and attacked, it didn't help so I ramped up to fungicide but it still seemed to be spreading. Then to my horror I noticed my beautiful tomato plants caught the powdery mildew! The Black Cherry and the SunGold in containers got it first, I assume because they were directly under the Crape Myrtle, then it spread to my other container with my Japanese Black Trifele and a Evista. Now it's starting to hit my in ground mater’s the Hillblilly, my favorite Japanese Black Trifele the in-ground one is setting fruit like crazy and out pacing every other tom.
I got out my ladder and cut out all the powdery mildew I could reach (the Crape is about twenty feet high.) And then I sprayed fungicide on all the remaining leaves my sprayer could reach with me standing on the highest rung of the ladder I could safely reach.
So now I'm truly depressed, I'm trying to do whatever I can to save as many of my toms as I can or at least stave off the mildew until I can get some fruit from my labors.
I am out there early morning now pulling off all the infected leaves I can find on my toms and then spraying Actinovate or fungicide. I have almost denuded my Black cherry it's breaking my spirit to be sure, but I haven't given up. If you guys can think of anything else I should be doing I sure will try it. Thanks for listening to my tale of woe.
keep your chin up, and remember that there's always next year! 
I'm praying for your plants ! Also, eating pasta...