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How to Manage Pests

UC Pest Management Guidelines

Root damaged by corky root..


Corky Root Rot

Pathogen: Pyrenochaeta lycopersici

(Reviewed 1/08, updated 1/08)

In this Guideline:


Infected roots of plants with corky root rot are distinctly corky. Extensive brown lesions, often arranged in bands with lengthwise cracking of the cortex, develop on the larger roots. The tips of infected older roots are pinched off. Small feeder roots may be completely decayed. Infected plants are stunted and slow growing. Branches on mature plants may die back from the tips.


The fungus survives for long periods as microsclerotia. Potential alternate hosts include cucurbits, peppers, safflower, and solanaceous weeds such as on nightshades. Corky root is generally a problem in early plantings under cool conditions. Disease development is optimal at 60° to 68°F (15.5° to 20°C). Corky root usually does not kill plants, but may reduce yields.


Cultural practices, or soil fumigation on fields with a history of corky root rot, will help to minimize problems from this disease.

Cultural Control
Plant when soils are warm in spring. Avoid consecutive crops of tomatoes. Although not extensively tested in California, soil solarization has been used to control corky root rot in other areas of the world. Rotate with nonhost crops.

Organically Acceptable Methods
Cultural control is acceptable in an organically certified crop.

Treatment Decisions
In fields with a history of corky root rot, a preplant treatment with metam sodium may reduce disease in a subsequent tomato crop.

Common name Amount/Acre** R.E.I+
(trade name)   (hours)

  Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to environmental impact Not all registered pesticides are listed. Always read label of product being used.
  (Vapam) 50–75 gal 48
  (Metam Sodium, etc.) 50–100 gal 48
  COMMENTS: Fumigants such as metam sodium are a source of volatile organic compounds (VOCs) but are minimally reactive with other air contaminants that form ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
**  See label for dilution rate.
+ 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.
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.
* Permit required from county agricultural commissioner for purchase or use.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Tomato
UC ANR Publication 3470
R. M. Davis, Plant Pathology, UC Davis
G. Miyao, UC Cooperative Extension, Solano/Yolo counties
K. Subbarao, USDA Agricultural Research Station, Salinas
J. J. Stapleton, UC IPM Program, Kearney Agricultural Center, Parlier
Acknowledgments for contributions to the disease section:
B. W. Falk, Plant Pathology, UC Davis

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