Your Pinwheel zinnias are immune to Powdery Mildew. That is a good thing. The Zaharas and Profusions are other strains of zinnias that are immune to Powdery Mildew. I grow Zinnia elegans and Zinnia hybrida, which are not immune to Powdery Mildew. So I occasionaly spray my zinnias with a systemic fungicide to prevent Powdery Mildew and a couple of other zinnia diseases.
This is a picture of a couple of my breeder zinnias.
ZM
