Listed below are specific host symptoms. The fungus attacks the basal crown and petioles. Plants appear to suddenly wilt and collapse in the field. Leaves wilt and fall from the head in succession. The heart may remain erect, but becomes a wet, slimy mass.
Sclerotinia can function either as soilborne or airborne pathogens.
At certain times of the year, depending on the inherent nature of the fungus and various environmental factors, the sclerotia germinate and form either mycelium which can infect a host, or an apothecium. Infection of host plants by mycelium can occur at or beneath the soil-line. Sclerotia germinate in the presence of exogenous nutrients and produce hyphae which invade nonliving organic matter, forming mycelium which then infects living host tissues. Penetration of the host cuticle is achieved by mechanical pressure. Mycelium infection is unlikely to infect plants located more than 2 cm from a sclerotium.