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How to Manage Pests
UC Pest Management Guidelines
Carrot
Cavity Spot
Pathogen: Pythium sulcatum and P. violae
(Reviewed 10/05,
updated 10/05)
In this Guideline:
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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.
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.
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) |
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| A. |
MEFENOXAM |
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(Ridomil Gold) EC |
See comments
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MODE OF ACTION: A phenylamide (Group 4)1 fungicide. |
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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. |
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| B. |
METAM SODIUM* |
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(Vapam, others) |
Label rates
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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. |
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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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