Crown Rot or Southern Blight or Southern Stem Rot -- Sclerotium rolfsii
Host: Creeping thyme, hosta, iris (all species), Narcissus spp., pittosporum, tulip.
Symptoms: The symptoms for crown rot vary by host. In rhizomatous iris, rotting at the base of the leaves near the soil line causes gradual dieback at tips of the outer leaves. In bulbous iris, rot of the bulb or stem and leaves just above the bulb causes the plant to yellow, stunt and die prematurely. In narcissus, the surface of the bulb becomes covered with a coarse, white growth that can contain small, reddish-brown sclerotia (survival structure). In tulips, the lower stems and bulb rot and typically are covered with white, threadlike mycelium. The leaves turn red and the plant eventually wilts and dies.
Conditions Favoring Disease: This disease is favored by moist, warm soil and overhead irrigation or rainfall.
How Pathogen Survives/Disperses: Sclerotia overwinter in the soil or in infected plant parts and may survive for many years in the soil.
Photo and write up provided by Syngenta Professional Products