Downy leafspot on hickory (Carya spp.) and walnut (Juglans spp.) is produced by the fungus Pseudomicrostroma juglandis (syn. Microstroma juglandis). The connection to walnut is clearly evident by the fungal pathogen's specific epithet. However, I most often see this disease on hickory growing in deep woods.
I've long admired silver linden with its dark green leaves accentuated by silver undersides. This tough tree is able to handle many of the urban slings and arrows that send less hardy trees to wood chippers. However, this eastern European native seems to be having a growing challenge with our native basswood lace bugs.