Agriculture: Tomato Pest Management Guidelines

Phytophthora Root Rot

  • Phytophthora parasitica and P. capsici
  • Symptoms and Signs

    The most distinctive symptoms of Phytophthora root rot are the brown lesions on roots of all sizes. The xylem of the roots above the lesions often turns yellowish or brown. In severe cases, nearly all roots may be girdled or rotted off. Aboveground, infected plants are slow growing and may wilt or die in hot weather. When fruit in contact with the ground are infected, the disease is called buckeye rot. Symptoms include tan or brown spots with concentric rings. Phytophthora capsici also causes greasy, purple-brown stem lesions.

    Comments on the Disease

    Phytophthora parasitica and P. capsici occur in most soils. Infection of plants occurs at any stage of growth when there is free water in the soil. Damage is greatest in poorly drained, compacted, or overirrigated soils.

    Management

    Good water management is key to managing this disease and avoiding the need for fungicide treatments.

    Cultural Control

    Provide good drainage and prevent flooding. Avoid wide fluctuations in soil moisture, which predisposes plants to infection. Keep tops of bed dry to avoid buckeye rot of the fruit. Planting cereals as a rotation crop may reduce the level of infestation in the soil. Resistant varieties are not yet commercially available.

    Organically Acceptable Methods

    Cultural control is acceptable in an organically certified crop.

    Chemical Control

    Fungicides are needed only in poorly drained soils or where root rot is historically a problem.

    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.
     
    A. MEFENOXAM
      (Ridomil Gold SL) 1 pt 48 7
      MODE OF ACTION GROUP NAME (NUMBER1): Phenylamide (4)
      COMMENTS: Follow application with an irrigation (see label).
    ** 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.
    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.
    Text Updated: 12/13
    Treatment Table Updated: 12/13