& Trotter, (1912) Albugo occidentalis, the causal agent of spinach white rust, is an oomycete plant pathogen, although some discussions still treat it as a fungal organism.

Albugo occidentalis is one of the most important spinach diseases in North America, found throughout the United States east of the rocky mountains.

It is unrelated to the basidiomycete rusts biologically, but appears somewhat similar on the surface of the leaf, sometimes causing the plant to form white or yellow blister-like pustules on leaves.

The early stage, a milder chlorosis, is found on the on abaxial face, but if the white rust is allowed to thrive, it can blister and be visible on the adaxial surface as well.

The oospore can overwinter in the soil, and in the spring it produces zoospores which will encyst on the surface of spinach leaves in the presence of water and germinate.