Help with leaf issue ID - could this be russet mites?

[MSchep]

Hi All,
Seeking some help identifying what is going on with these lower leaves on my sungold plant. This is an issue i usually see every year a little bit later in the season, but spreads pretty steadily. I've never really figured out what it is or how to treat. Early this season, I read some of the threads here on russet mites, and I've been wondering if that is actually the problem I've been having?

Several leaf pics follow of troubled spots I've just removed from the plant, the first two are the same leaf, top and bottom. I added a close up of one of the cut stems for good measure, though I don't see anything there.

Thanks in advance for your thoughts...