Powdery mildew on yarrow AND goldenrod -- applied horsetail fungicide

A week or two ago I noticed what looked like powdery mildew on the yarrow (the volunteer in the patio stones next to my chair which started growing last year), so I sprayed it with the horsetail fungicide.  Google says yarrow is susceptible to PM so I do imagine that's what it is.

Lately I've noticed more of it, so, I sprayed it again today.  (This is still with the original batch I whipped up a few weeks ago.)

And today I noticed the goldenrod (the volunteer in front of the hose well which started growing last year) also has white powdery specks on the leaves, so I sprayed it too.  And Google says goldenrod is also susceptible to PM.

So far not seeing signs on the squash/zucchini, but it's early days yet... (haven't sprayed them with the fungicide yet)