Thielaviopsis root rot, caused by the fungal pathogen Thielaviopsis basicola, can occur in over 150 species of greenhouse and perennial crops, including astilbe, begonia, calla lilies, calibrachoa, cyclamen, fuchsia, gaillardia, geranium, gerbera, kalanchoe, lupine, pansy, penstemon, peony, petunia, phlox, poinsettia, primula, snapdragon, strawberry, sweet pea, tobacco, tomato, verbena, vinca and viola.
Thielaviopsis root rot is characterized by dark brown or blacked spores within the root, followed by black lesions on the root, which give the characteristic name of “black root rot”. It is a difficult disease to control once it is started, so it is best to discard infected plants. Crop loss from Thielaviopsis can be quite extensive if not controlled.