How to Manage Pests

UC Pest Management Guidelines

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	R.E.I.+	P.H.I.+
(trade name)			(hours)	(days)
When choosing a pesticide, consider information relating to environmental impact.
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 (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) 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 actions (for more information, see http://www.frac.info/). Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode of action Group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode of action Group number; for fungicides with other Group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode of action Group number.

PUBLICATION

UC IPM Pest Management Guidelines: Celery
UC ANR Publication 3439
Diseases
S. T. Koike, UC Cooperative Extension, Monterey County
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Imperial County
Acknowledgment for contributions to Diseases:
R. L. Gilbertson, Plant Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara County

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