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UC Pest Management Guidelines

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Carrot

Southern Blight

Pathogen: Sclerotium rolfsii

(Reviewed 1/09 , updated 10/05 )

In this Guideline:

SYMPTOMS AND SIGNS

Southern blight is characterized by a soft watery decay of the taproot at or near the soil line. The disease develops rapidly, resulting in wilting and yellowing of the carrot top. White mats of mycelium develop on the carrot root and in the adjacent soil. Tan to brown round sclerotia (resting structures) about the size of a mustard seed (0.06 inch) develop on mycelial mats. The abundant sclerotia are a good diagnostic feature of southern blight.

COMMENTS ON THE DISEASE

High temperatures (46° to 99°F) favor the disease. The fungus attacks a wide range of plants and survives for long periods in the soil as sclerotia. However, southern blight is usually a minor disease of carrots.

MANAGEMENT

Cultural Control

Rotation to nonhosts such as corn or small grains for at least 2 years reduces numbers of sclerotia. Burying plant refuse helps destroy sclerotia.

Organically Acceptable Methods

Cultural controls are acceptable for use on organically grown produce.

Treatment Decisions

Chemical control is not recommended.

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Carrot
UC ANR Publication 3438

Diseases

J. Nunez, UC Cooperative Extension, Kern County
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Fresno County
Acknowledgment for contributions to Diseases:
B. W. Falk, Plant Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara County

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