How to Manage Pests

UC Pest Management Guidelines

SYMPTOMS

Sclerotinia infection may occur at any stage of growth, and extensive root decay may occur before symptoms of wilt and collapse appear on the upper part of the plant. Infection is always accompanied by a characteristic cottony, white mycelium that appears on the surface of the infected tissues. On or inside the white mycelium appear black, round-to-irregular-shaped structures (sclerotia), which are about 0.1 to 0.4 inch wide. Sclerotia are survival structures of the fungus. The fungi Pythium or Rhizoctonia may also produce cottony growth, but will not produce sclerotial bodies in the mycelium. Sclerotinia soft rot is usually soft and watery compared to Rhizoctonia rot, which tends to be firm and dry. Bacterial soft rot tends to be slimy and malodorous and is often secondary to Sclerotinia and other fungal rots.

COMMENTS ON THE DISEASE

Sclerotinia is most active when soil temperatures are 55° to 77°F. Moist soils are necessary for fungal activity. However, once infection is established, moisture from the carrot root tissue is sufficient to maintain fungal growth.

MANAGEMENT

Cultural Control
Deep plowing once per year to bury sclerotia 8 to 10 inches into the soil will reduce disease incidence, but not eliminate it completely because spores may be blown in from other fields. A 3-year rotation to cereals, corn, or cotton will also help reduce sclerotial populations in the soil. Trimming the sides of the foliage after the canopy closes may increase ventilation between rows and allow leaves to dry.

Organically Acceptable Methods
Cultural controls are acceptable for use on organically grown produce.

Monitoring and Treatment Decisions
Begin applications when disease first appears and conditions favor disease development.

PUBLICATION

UC IPM Pest Management Guidelines: Carrot
UC ANR Publication 3438
Diseases
R. M. Davis, Plant Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara Co.
J. Nunez, UC Cooperative Extension, Kern Co.
T. A. Turini, UC Cooperative Extension, Imperial Co.
Acknowledgment for contributions to the diseases section:
B. W. Falk, Plant Pathology, UC Davis

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