|Drooping snapdragons in flower bed. Jan 23, 2012.|
|Stem lesions and visible white mold, evidence|
of the causal fungus, Sclerotinia sclerotiorum.
Because the fungus produces airborne spores, it can sometimes even blow into greenhouses and cause stem rots on ornamentals and "collar rot" on tobacco. This is one reason it's so important to avoid leaving piles of dead plant material in and around greenhouses. Of course diseased plant material should never be composted, in this case because of the durability of the sclerotia.
Nota bene! Ojo! Vorsicht! This disease is completely different from Southern blight (Southern stem blight) caused by the unrelated fungus Sclerotiuim rolfsii. The scientific names of the fungi are confusingly similar, both cause stem rots, and both produce visible white mycelium on the plant, but there are key differences. Southern blight occurs from late spring through the heat of summer, not in the winter and early spring. Also, the mature sclerotia of Sclerotium rolfsii are tiny, round, and tan-colored (rather like radish seeds), whereas those of Sclerotinia are somewhat larger, irregular in shape, and black. Both kinds are white on the inside when cut open, and both take longer to form than the mycelium itself.
|Above: Sclerotia of Sclerotinia sclerotiorum|
(Photo: PP Dept. Slide Collection)
|Above: Sclerotia of Sclerotium rolfsii|