Agriculture: Tomato Pest Management Guidelines

Corky Root Rot

  • Pyrenochaeta lycopersici
  • Symptoms and Signs

    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.

    Comments on the Disease

    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 (15.5–20°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 per acre** REI‡ PHI‡
    (Example trade name) (hours) (days)
    Not all registered pesticides are listed. The following are ranked with the pesticides having the greatest IPM value listed first—the most effective and least likely to cause resistance are at the top of the table. When choosing a pesticide, consider information relating to the pesticide's properties and application timing, honey bees, and environmental impact. Always read the label of the product being used.
      (Vapam HL) 50–75 gal See label NA
      (Metam CLR 42%, etc.) 50–75 gal See label NA
      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.
    ** See label for dilution rate.
    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 until harvest can take place. In some cases the REI exceeds the PHI. The longer of these two intervals is the minimum time that must elapse before harvest may take place.
    * Permit required from county agricultural commissioner for purchase or use.
    1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of action. 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.
    NA Not applicable.
    Text Updated: 12/13
    Treatment Table Updated: 12/13