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SYMPTOMS OF FUNGAL DISEASES

Fungi cause a wide variety of ROTS. Rots involve the wholesale destruction and disintegration of a large portion (if not all) of a plant. Typically, affected plant parts become discolored and soft. Common fungal rots include crown rots (shown in this photo), where the crown of the plant is affected, and root rots, where root tissue is infected and degraded.

The disease shown in this picture is southern blight caused by the fungus Sclerotium rolfsii. This disease is one that has traditionally been associated with warmer climates and the fungus is not thought to survive harsh Wisconsin winters. However, the Plant Disease Diagnostics Clinic at the UW-Madison has seen an increase in the number of cases of this disease during the 1998 and 1999 growing seasons. In some cases, the pathogen appears to have been introduced into Wisconsin on ornamentals that were produced in the south. In other situations, there is some evidence suggesting that the pathogen may have been introduced in mulch. Finally, there is also some evidence to suggest that the pathogen may have survived at some sites in Wisconsin during the mild winters of 1997/1998 and 1998/1999. To identify this disease, look for white mycelia on the surface of unthrifty plants near the base. Imbedded in the mycelia, you will find small tannish to reddish seed-like objects (see white arrow). These seed-like objects, called SCLEROTIA (singular = SCLEROTIUM), are masses of tightly packed hyphae that serve as resting/survival structures for the fungus.