Brown Edge on River Birch Leaves

My young river birch have brown rusty edges on some of the lower leaves. It looks like a fungal infection, probably from the humid weather (and made worse when I water the lawn in the evening after work). I cut a few of the bottom branches off anyway to promote vertical growth, so that should get rid of a lot of the infected leaves. I'm also going to spray fungicide on the entire tree to hopefully prevent it from getting out of hand before Fall.

Looks like rust, or advanced leaf blight, a fungal infection on the leaves from humid weather and watering in the evenings

It's spreading! Only on the lower branches so far. The new leaves at the ends of the branches are fine, and the upper leaves look okay.

Brown spots with a yellow halo, looks like a sure sign of leaf blight