Symptoms and Signs
Crater rot symptoms are usually restricted to the lower portions of the celery petioles where soil is in contact with plant tissue. Early symptoms consist of small, irregular, reddish-brown lesions that develop on outer and inner sides of the lower petioles. Developing lesions expand and become brown, sunken spots or craters. These lesions remain firm and dry unless secondary decay organisms invade and cause soft rots. With a hand lens, the dark brown, mycelia of Rhizoctonia solani may sometimes be seen within and on the margins of the lesions.
Comments on the Disease
Rhizoctonia solani is a soilborne fungus that can persist in the soil for long periods of time. It infects many plant hosts and can also survive on decaying organic matter in the soil. This pathogen can survive in soil by forming tight masses of mycelium (sclerotia) that resist desiccation. Warm and moist soil conditions are needed for crater spot development.
Management
Cultural Control
Place transplants at proper planting depth. Planting too deeply can increase disease severity and incidence. Manage irrigations to avoid overly wet soils. Do not plant into fields with large amounts of undecomposed plant residue. During soil cultivation, avoid throwing soil onto the crowns of plants.
Organically Acceptable Methods
Cultural controls are acceptable for use on organically grown produce.
Monitoring and Treatment Decisions
If monitoring indicates crater rot is developing on the plants, protectant fungicides are sometimes necessary. Direct these sprays to the base of the celery plants.
| Common name | Amount to use | 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. | CHLOROTHALONIL | |||
| (Bravo Ultrex) | Label rates | 12 | 7 | |
| (Echo 720) | 12 | 7 | ||
| MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M5) | ||||
| ‡ | Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. 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. |