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.
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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