Southern Blight
Sclerotium rolfsii Sacc.  
southernblightncrfig83.jpg (22812 bytes)
Mycelium of southern blight fungus on infected apple rootstock.
Developing sclerotia of S. rolfsii on apple rootstock tissue.

I. Introduction: Southern blight, caused by the fungus Sclerotium rolfsii Sacc., is primarily a problem in the Piedmont apple growing region in the southeastern U.S. Sclerotium rolfsii is a widespread pathogen that affects several hundred plant species.

II. Symptoms and Disease Cycle: Sclerotium rolfsii affects the lower stems and roots of apple trees, killing the bark and girdling the trees. The disease is characterized by the presence of a white, web-like mycelium, which often forms at the bases and on the lower stems of affected trees. Tree death usually occurs rapidly.   Light brown to yellow, round sclerotia 1/16 to 1/8 inch in diameter form in the mycelial mat. The fungus is spread by the sclerotia, which also serve as overwintering structures. The disease is most severe on 1- to 3-year-old trees. As the bark thickens, trees become resistant to infection.

IV. Monitoring: There is no monitoring schedule for southern blight.

V. Management:  Avoid planting sites where the disease has been severe on previous crops such as peanuts, clover, tomato, and soybean. Keep the soil around the bases of trees free of dead organic matter that may serve as a food base for S. rolfsii. Some differences exist in rootstock susceptibility. The most resistant rootstock currently used is M.9. No fungicides are currently registered on apples for southern blight control

Text prepared by A. L. Jones and T. B. Sutton

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