Sclerotinia sclerotiorum is best identified by observation of the ascoma. The ascoma is apothecioid in shape and yellow-brown to tan in color. Apothecia are not formed on a stroma, rather they arise from a sclerotium produced by mature hyphae. Apothecia produce asci that will stain blue when exposed to iodine. Sclerotia formed by this fungus are large, irregular in shape, and dark-brown to black in color. This fungus can be partially identified on plant material by the production of a white fluffy mycelium.