How to Manage Pests

UC Pest Management Guidelines


Cavity Spot

Pathogens: Pythium sulcatum and P. violae

(Reviewed 1/09, updated 9/12, pesticides updated 4/16)

In this Guideline:


Cavity spot is characterized by elliptical to irregularly shaped depressed lesions oriented across the mature carrot taproots. 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 taproot, 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.


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, blackeyedpeas, wheat, cucumber, beets, and other plants, including weeds, may not result in symptoms. Nonhosts include tomato, cotton, watermelon, corn, and potato.


Cultural Control

Practice 3-year crop rotations with crops other than alfalfa or carrots. Do not over-irrigate. 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 a history of severe cavity spot.

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees, and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
  (Ridomil Gold SL) See comments 48 7
  COMMENTS: Apply 1–1.3 pt/acre as a preplant incorporated treatment or as a soil surface spray immediately after planting. Beginning 28 to 50 days after planting, apply Ridomil Gold SL on a 14- to 21-day interval. Apply 0.25 to 1 pt/acre in water by chemigation or by ground equipment with a spray directed to the base of the plant or shanked in with liquid fertilizer. Follow all ground applications with an irrigation of one inch of water to promote movement of material into the root zone. Refer to the Ridomil Gold SL label for use directions for chemigation. Do not exceed 2.8 pt/acre per crop season.
  (Reason 500SC) 8.2 fl oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
  COMMENTS: Alternate with a mefenoxam fungicide such as Ridomil Gold SL. Apply at a 14- to 21-day interval.
  (Ranman) 6.0 fl oz 12 14
  MODE-OF-ACTION GROUP NAME (NUMBER1): ubiquinone reductase, Qi site (21)
  (Presidio) 3–4 fl oz 12 7
  MODE-OF-ACTION GROUP NAME (NUMBER1): Mitosis and cell division (43)
  (Vapam) Label rates See label NA
  COMMENTS: Apply preplant by sprinkler, drip irrigation, or flood irrigation. Check label for rates and preplant timing. Fumigants such as metam sodium are a source of volatile organic compounds (VOCs) but are minimally reactive with other air contaminants that form ozone.
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 actions. 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.
* Permit required from county agricultural commissioner for purchase or use.
NA Not applicable.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Carrot
UC ANR Publication 3438


J. Nunez, UC Cooperative Extension, Kern County
R. M. Davis, Plant Pathology, UC Davis
T. A. Turini, UC Cooperative Extension, Fresno County

Acknowledgment for contributions to Diseases:
B. W. Falk, Plant Pathology, UC Davis
F. F. Laemmlen, UC Cooperative Extension, Santa Barbara County

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