Powdery Mildew?

Started noticing some white powdery substance on the tops of some hop leaves on my Centennial plant (1st year, already about 10 feet tall). Tried to rub it off but it was kind of stuck on there. I dosed the leaves with some insecticidal soap last week - maybe this is some residue that dried on there? Concerned that if it's powdery mildew it will spread and take out the best rhizome I have this year.

I've attached pictures - thoughts?

That is not powdery mildew, just water spots. Nothing to worry about. Notice how the marks are concentrated around the edges of the leaf? At the tip of each of the serrations of the leaf there is a vein, which ends in something called a hydathode, which will put out a drop of water + nutrients in the early morning when the humidity is high. That drop will dry, leaving the nutrients behind as salt. The salt usually means you might be fertilizing too much.

Awesome - great info. I've only fertilized once about 3 weeks ago... and its only showing up on one of my plants. I'll assume it'll be ok if I just leave it be. Thanks for your help!