As corm infections progress, the brown discolored area becomes larger and more pronounced. However, the edge of the infected area remains diffuse and has no distinct border with the healthy tissue. In advanced stages, rots are brown to purplish. These sporangia release swimming spores called zoospores when water or sufficient moisture is present. The sporangia can also germinate directly by producing germ tubes that penetrate the host.
Zoospores are able to swim for hours and are attracted to organic matter or host tissue.
This pathogen has two mating types, A1 and A2. When grown together in culture dishes, sexual spores called oospores are formed. These oospores are thick walled and may serve as survival structures in the absence of the host. However, oospores have not been found in nature. This pathogen grows well between 68 to 77 F. Moisture favors the growth, sporulation, dissemination, and infection processes of this pathogen.