Agriculture: Cole Crops Pest Management Guidelines

Ring Spot

  • Mycosphaerella brassicicola
  • Symptoms and Signs

    In California, this disease occurs primarily on Brussels sprouts. Symptoms consist of circular leaf spots (0.5 inch in diameter) that range in color from light brown to black. With time, these spots develop concentric rings, much like a target pattern. Small, spherical fruiting structures may also be observed within the leaf spots. If disease is severe, some defoliation may take place. This pathogen may also infect the sprouts, causing dark lesions on outer leaves.

    Comments on the Disease

    The infection and disease development are favored by cool, moist conditions. Spores produced by this pathogen are spread by wind. Mycosphaerella brassicicola will persist in soil on infected plant residues only. There is some evidence that this pathogen may be carried on seed.

    Management

    Incorporate plant residues so that infected material decomposes fully. Remove volunteer plants that may be infected. Plant disease-free transplants. If ring spot is a problem in the area, use a protectant fungicide before infection takes place.

    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. CHLOROTHALONIL
    (various products) Label rates 12 7
    MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
    COMMENTS: Use at 7- to 10-day intervals; multiple applications are needed (up to 4 maximum).
    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 to harvest. In some cases the REI exceeds the PHI. The longer of the two intervals is the minimum time that must elapse before harvest.
    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. For fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17, make no more than one application 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 a fungicide with a different mode-of-action group number.
    Text Updated: 06/07
    Treatment Table Updated: 11/08