Southeastern Apple Production

Plant Pathology

Disease Management

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).

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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.

Recommendations for the use of agricultural chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by North Carolina Cooperative Extension nor discrimination against similar products or services not mentioned. Individuals who use agricultural chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical. For assistance, contact your county Cooperative Extension agent.

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Turner Sutton
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Format updated March 29, 2011