thanks for the quick reply! Powdery mildew was my first thought as well because I have heard about it so much on zinnia. I spent a bit of time looking at google images and noticed a few differences. On my plants there is nothing on the leaf surface that I can physically remove with my fingers. Also the brown color seems to follow the leaf structure and form around the veins in the leaf, instead of being random and covering the leaf. It very well could still be powdery mildew as I have never seen it in person and have no experience with it. I will go ahead and get a fungicide and give it a try because even if this is not powdery mildew I am sure I will see it later on with our wet summers. Thanks again!