Symptoms and Signs
Sclerotinia infection may occur at any stage of growth, and extensive root decay will occur before symptoms of wilt and collapse appear on the above ground of the plant. Infection is always accompanied by a characteristic cottony, white mycelium that appears on the surface of the infected tissues, usually near the soil line. On or inside the white mycelium appear black, round to irregular-shaped structures (sclerotia), which are about 0.1 to 0.4 inch (0.3–1 cm) in length. Sclerotia are survival structures of the fungus.
Comments on the Disease
Cottony soft rot is favored by wet, cool weather, when soil temperatures are 55° to 70°F. During prolonged wet, cool conditions, the fungus can produce airborne spores. However, infections resulting from soilborne inoculum are more common in most parts of California. Moist soils are necessary for fungal activity, but once infection is established, moisture from the carrot root tissue is sufficient to maintain fungal growth. The disease can also occur in storage carrots from infections that initiated in the field, from uncleaned pallet boxes, or from contamination in storage.
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 2-year rotation to cereals, corn, or cotton will also help reduce sclerotia numbers in the soil. Trimming the sides of the foliage after the canopy closes and effective weed control may provide a less favorable environment for disease development by increasing ventilation between rows. Ensure proper storage conditions with near freezing temperatures, high relative humidity, and proper air movement.
Organically Acceptable Methods
Use cultural controls in a certified organic crop.
Monitoring and Treatment Decisions
Begin applications when disease first appears, and conditions favor disease development.
| Common name | Amount per acre | REI‡ | PHI‡ | |
|---|---|---|---|---|
| (Example trade name) | (hours) | (days) | ||
| Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used. | ||||
| A. | BOSCALID | |||
| (Endura) | 7.8 oz | 12 | 0 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Succinate dehydrogenase inhibitor (7) | ||||
| COMMENTS: Begin application prior to disease development and continue on a 7- to 14-day interval. Use a shorter interval when disease pressure is high. To limit the potential for resistance development do not apply more than two sequential applications before rotating to a labelled fungicide with a different mode of action. | ||||
| B. | FLUAZINAM | |||
| (Omega 500F) | 16 fl oz | 12 | 7 | |
| MODE-OF-ACTION GROUP NAME (NUMBER1): Uncouplers of oxidative phosphorylation (29) | ||||
| COMMENTS: Make the initial application approximately 45 days prior to harvest or earlier if disease appears. If required, a second application can be made 14 days after the initial application. Apply in 30 to 50 gallons of water per acre as a directed band spray over the crop. DO NOT make more than 4 applications at the rate of 16 fl oz of Omega 500F per crop cycle. | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without personal protective equipment. Preharvest interval (PHI) is the number of days from treatment to harvest. In some cases, the REI exceeds the PHI The longer of two intervals is the minimum time that must elapse before harvest. |
| 1 | Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. Fungicides with different group numbers are suitable to alternate in a resistance management program. In California, make no more than one application of a fungicide with a mode-of-action group number associated with high resistance risk before rotating to a fungicide with a different mode-of-action group number; for other fungicides, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action group number. |