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How to Manage Pests

UC Pest Management Guidelines


Cavity spot-induced, irregularly shaped lesions across mature carrot tap roots.

Carrot

Cavity Spot

Pathogen: Pythium sulcatum and P. violae

(Reviewed 10/05, updated 10/05)

In this Guideline:


SYMPTOMS

Cavity spot is characterized by elliptical to irregularly shaped, depressed lesions oriented across the mature carrot tap roots. Individual lesions are usually less than 0.5 inch (1.3 cm) in diameter, but can be much larger, especially on processing varieties. Infections occur anywhere along the tap root, but lesions tend to be more abundant on the upper third of the root and are often found where lateral roots emerge from the taproot. Lesions begin as pinpoint, sunken spots and generally enlarge as roots mature.

COMMENTS ON THE DISEASE

The causal fungus is favored by cool soil temperatures; in culture it grows best at 58°F. The incidence of the disease is probably dependent on the number of thick-walled oospores (overwintering spores) in the soil. Pythium sulcatum and P. violae also cause lesions on alfalfa roots. Infections of other hosts such as celery, blackeye beans, wheat, cucumber, and beets may not result in symptoms. Nonhosts include tomato, cotton, watermelon, corn, and potato.

MANAGEMENT

Cultural Control
Practice 3-year crop rotations with crops other than alfalfa or carrots. Do not overirrigate. Harvest carrots soon after they mature because older carrots are more susceptible to infection. All carrot varieties are susceptible.

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

Treatment Decisions
Treat fields with histories of severe cavity spot.

Common name Amount/Acre
(trade name)  

A. MEFENOXAM  
  (Ridomil Gold) EC
See comments
  MODE OF ACTION: A phenylamide (Group 4)1 fungicide.
  COMMENTS: Apply 1–2 pt/acre as a preplant incorporated treatment or as a soil surface spray immediately after planting. Postplant use is allowed under a Special Local Needs label. Make a second application of 12 fl oz/acre 40–50 days after planting. If needed, a third application of 12 fl oz/acre can be applied 14–21 days after the second application. Do not exceed more than 2.8 pt/ acre/crop season or harvest within 7 days of treatment.
     
B. METAM SODIUM*  
  (Vapam, others)
Label rates
  COMMENTS: Apply preplant by sprinkler, drip irrigation, or flood irrigation. Check label for rates and preplant timing. Fumigants, such as metam sodium and 1,3-dichloropropene, are a prime source of volatile organic compounds (VOCs), which are a major air quality issue. Fumigate only as a last resort when other management strategies have not been successful or are not available.
 
     
1 Group designations are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group designation are suitable to alternate in a resistance management program. For more information, see http://www.frac.info/.
* Permit required from county agricultural commissioner for purchase or use.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

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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Statewide IPM Program, Agriculture and Natural Resources, University of California
All contents copyright © 2005 The Regents of the University of California. All rights reserved.

For noncommercial purposes only, any Web site may link directly to this page. FOR ALL OTHER USES or more information, read Legal Notices. Unfortunately, we cannot provide individual solutions to specific pest problems. See How to manage pests, or in the U.S., contact your local Cooperative Extension office for assistance. /PMG/r102100411.html revised: October 28, 2005. Contact webmaster.