Assuming those “small circular particles” are around 4-5 µm diam., they are consistent with conidia referred to as Coniothyrium concentricum. However, it is likely to be a species complex, and related to Paraphaeosphaeria species that have also been implicated in leaf spotting of Yucca. So use the name if you like, but be aware that it is only an approximate identification.
The species is included in FRDBI as Microsphaeropsis concentrica, but both Coniothyrium and Microsphaeropsis are dustbins containing species with similar small brown conidia.
Enjoy…
