Kinda looks like it is coated with powdery mildew, though I've never seen
it get THAT bad. If that's not a powdery coating then it's not powdery
mildew. But if that IS what it is, it won't necessarily kill the clump if
it was otherwise going to perennialize. But you'll have to clip the
infected plant to the ground, discard rather than compost the infected
leaves, clean up the area super-well, trim back surrounding plants to
permit better air circulation & better sun exposure, & water from the
ground rather than with overhead sprinklers. Spray any autumn regrowth
with dilute milk to keep the powdery mildew at bay, & in spring when the
clump returns in earnest, give it another milky spraying, which works far
better than do chemical fungicides on powdery mildew.

Thanks Paghat! Looking around my garden, it would appear that I have
more of this stuff on my boston ivy. Where does this stuff come from
and how is it spread from place to place in my garden? Is there any
way to eradicate it once and for all?

-Fleemo