Potato Diseases click on any image to see larger Peeled potato tuber showing infection by Phytophthora infestans Late blight lesion on potato stem Late blight lesion and sporulation of P. infestans on potato stem Late blight infection on peeled potato tuber Late blight lesions on potato leaflets Immature sclerotia developing on belowground stem Black dot Sclerotia on dried stems Fruiting bodies of a bird nest fungus. Do not confuse with apothecia of Sclerotinia. Sclerotinia lesion on the inflorescence stalk of a potato plant. The infection originated from a blossom contaminated with an ascospore. The ascospore germinated and mycelium reached the stalk before the blossom dropped. An apothecium on soil and sclerotia of Sclerotinia sclerotiorum on a bean pod. Mycelium of Sclerotinia sclerotiorum growing from dead potato foliage forming a mycelial mat on the soil surface. Any green potato foliage that may become lodged on the mycelial mat will become infected if sufficient moisture is present. Sclerotinia lesion at the base of a potato stem. Lesions that girdle the stem near the soil surface may substantially reduce yield. Young sclerotia of Sclerotinia sclerotiorum in stem of an ornamental squash. Young Sclerotinia lesion developing on a potato stem showing plant debris from which served as a substrate for ascospores to germinate, produce mycelium and infect the stem.