Collar rot first appears as small, dark green, water-soaked lesions at the base of stems. Clusters of infected transplants will appear and will have a yellow, wilted, and unthrifty appearance.

Signs of the fungus are found normally at the base of plants or on debris in float trays and include a white, cottony mycelium (fungal mass), present if humidity is high, and irregularly shaped, black sclerotia. Sclerotia resemble seeds or rodent droppi

Plants can be rotted in half by complete rotting of a portion of the lower stem.

Lower stem of an infected plants which severely rotted.