How to Manage Pests
UC Pest Management Guidelines
Cottony Soft Rot
Pathogen: Sclerotinia sclerotiorum
(Reviewed 1/09, updated 1/09)
In this Guideline:
SYMPTOMS AND SIGNS
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 cottony soft 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.
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. Avoid planting into fields with a history of cottony soft rot.
Organically Acceptable Methods
Cultural controls and the use of the biological fungus, Coniothyrium minitans, are acceptable for use on organically grown produce.
Monitoring and Treatment Decisions
Begin applications when disease first appears and conditions favor disease development.
UC IPM Pest Management Guidelines:
Acknowledgment for contributions to Diseases: