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Southern Blight

Sclerotium rolfsii

Southern blight, caused by Sclerotium rolfsii, is most severe in recently planted orchards and nurseries, especially in the Piedmont growing regions of the Southeast.

Symptoms

The most distinct symptoms and signs occur at the collar of the tree. Small, round, light brown to yellow resting structures of S. rolfsii, known as sclerotia, often can be found appressed to the stem of the tree or in the soil adjacent to infected trees (Fig 1). If conditions are moist, a white web-like mycelial growth may also be present (Fig 2). Affected cortical tissues in the collar of the tree are often shredded . One to 3 year old trees are most susceptible; as the bark thickens on trees they become more resistant. Affected trees usually die suddenly. When trees die in the summer, leaves turn brown and often remain attached to the tree
(Fig 3).

Fig 1 - Sclerotia at base of tree> Fig 2 - Mycelial growth Fig 3 - Dead tree with leaves attached
Fig 1. Sclerotia at base of tree Fig 2. Mycelial growth Fig 3. Dead tree with leaves attached

Control

S. rolfsii affects many agronomic crops, including peanuts, soybeans, clover, and tomato; consequently, the disease tends to be most severe when apples are planted following these crops. Since dead organic matter serves as a food base for the fungus, clean cultivation will help reduce losses. Rootstocks vary somewhat in their susceptibility: M.9 and M.26 are most resistant. There are no chemicals registered for control of southern blight.

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Format updated March 29, 2011