Physoderma alfalfae is a soil-borne parasitic fungus that invades and destroys the crown region of budding alfalfa plants. This pathogen is a simplistic fungus lacking an integrated net-like structure and is comprised of only small, simple filaments that invade alfalfa host cells to obtain nourishment.

Crown wart disease mainly attacks the many-branched crown of alfalfa plants, which is partially embedded in soil. Infection causes abnormal growths called galls to form along the crown and is the site where reproductive resting spores are produced. During excessively wet conditions, the spores in the decaying crown release motile zoospores that swim to infect nearby plants.

Most crown rots involve more than one type of organism and are collectively referred to as crown rot complex, and positive identification of the culprits often requires laboratory examination. General symptoms of crown wart include deterioration, discoloration, and abnormal cell proliferation of infected tissue. The disease also causes unproductive and typically stunted shoots. Injury sustained from crown wart provides an entry point for other opportunistic bacteria, fungi, and insects.