Host: More than 360 plants, including Anemone coronaria, Aquilegia spp., begonia, calceolaria, ornamental pepper, chrysanthemum, dahlia hybrids, forsythia, gerbera, petunia, Gloxinia.
Symptoms: This fungus is most damaging in outdoor soils. However, it may cause root, crown and stem rots in greenhouses. White strands of mycelium form on infected plant parts. The mycelium produces a dense mat on the surface of the soil at the base of the plant. The foliage may also become infected when the leaves come in contact with the ground. Sclerotinia are black, lumpy structures that look like charcoal.
Conditions Favoring Disease: Infection by this disease is dependent on high soil moisture for an extended period of time. Outdoors, the growing area must be at moisture field capacity for 10 days before germination will occur.
How Pathogen Survives/Disperses: The primary source of infection, resistant fungal structures called sclerotia, are found in soil and plant debris. Optimum temperatures for germination of sclerotia are 55° to 59°F. Some germination may occur over a wider temperature range — 30° to 79°F.
Photo and write up provided by Syngenta Professional Products