What is the common name for the hop stunt virus?

The common name for the hop stunt virus is indeed "Hop stunt virus." This virus is a significant concern for hop growers because it can severely affect hop plants, leading to reduced yield and quality of hops used for brewing. The disease caused by this virus often manifests through symptoms such as stunted growth and distorted leaves, ultimately impacting the production of hop compounds critical for flavor and aroma in beer.

The other options listed refer to different entities in the realm of plant pathology. The hop mosaic virus is a distinct viral disease that also affects hops but is not the same as the hop stunt virus. Downy mildew and powdery mildew are both fungal diseases, with downy mildew primarily caused by the organism Pseudoperonospora humuli and powdery mildew being caused by various fungi like Erysiphe and Podosphaera species. These diseases, while problematic for hops, do not share the viral characteristics of the hop stunt virus. Thus, the correct designation for the virus in question is accurately represented by its common name, "Hop stunt virus."