Agriculture: Tomato Pest Management Guidelines

Bacterial Speck

  • Pseudomonas syringae pv. tomato
  • Symptoms and Signs

    Bacterial speck appears as dark brown to black lesions of various sizes and shapes on leaves, fruit, and stems. Tissue adjacent to the lesions is initially yellow. Leaf lesions are frequently concentrated near margins, causing extensive marginal necrosis (tissue death). Lesions on immature fruit are slightly raised and small, varying in size from tiny flecks to 0.125 inch (3 mm) in diameter and cause raised black spots on mature fruit. Fruit lesions are superficial, seldom penetrating more than a few cells deep.

    Comments on the Disease

    The bacteria survive in soil, in debris from diseased plants, and on seeds. Infection is favored by cool, moist weather. The pathogen is spread by splashing rain or sprinkler irrigation. Disease progress is stopped during hot weather. In severe cases, infected plants are stunted, which may result in a delay in fruit maturity and yield reduction.

    Management

    Cultural controls and copper spray generally provide adequate control of bacterial speck in early planting.

    Cultural Control

    • Delay planting in spring to avoid exposing tomatoes to cool wet conditions that favor disease development.
    • When the disease appears, change from overhead to furrow irrigation.
    • Do not plant tomatoes in a field previously planted to tomatoes that developed the disease; instead rotate with a nonhost crop such as small grains or corn.

    There are two races in California: Race 0 and Race 1. Many varieties are resistant against Race 0 but none currently possess resistance against Race 1, which is the predominant race throughout the state.

    Organically Acceptable Methods

    Cultural control and some copper formulations are acceptable for use on organically certified produce.

    Monitoring and Treatment Decisions

    Copper-containing bactericides provide partial disease control. Timing is critical. Apply before rainfall and repeat at 10- to 14-day intervals when cool and moist conditions prevail. Copper is strictly a protectant and must be applied before an infection period occurs. One or two treatments are usually enough to protect tomatoes during the most susceptible stages of growth. Spraying can stop when temperatures move into the 90°F range.

    Resistance or partial resistance to copper is common. This is somewhat overcome by combining copper with mancozeb.

    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. COPPER HYDROXIDE#
    (Kocide 3000) 0.75–1.75 lb 48 0
    MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
    COMMENTS: Not all copper compounds are approved for use in organic production; be sure to check individual products.
    B. COPPER HYDROXIDE#
    (Kocide 3000) 0.75–1.75 lb 48 0
    MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M1)
    . . . PLUS . . .
    MANCOZEB
    (Dithane M-45) 2 lb 24 5
    (Dithane F-45 Rainshield) 1.6 qt 24 5
    (Penncozeb 75DF) 1–1.5 lb 24 5
    MODE OF ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
    COMMENTS: The addition of mancozeb increases the efficacy of copper. Check with your processor concerning allowed materials and rates. Be sure to follow label directions on all products when making a tank mix; the most restrictive label precautions and limitations must be followed.
    ** 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.
    # Acceptable for use on organically grown produce.
    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