Agriculture: Cole Crops Pest Management Guidelines

Phytophthora Root Rot

  • Phytophthora megasperma
  • Symptoms and Signs

    The external surfaces and internal tissues of infected roots are water-soaked, dark in color, and rotted. Leaves (especially older ones) first turn purple-red, and later yellow, and then wilt. The plant may be stunted, and with time the entire plant wilts. The stem near the soil line may turn black and become soft.

    Comments on the Disease

    Phytophthora root rot occurs on cauliflower, Brussels sprouts, and other crucifers in the coastal areas. It usually occurs only if cole crops are planted in poorly draining, fine-textured soils that are kept overly wet. Hence, root rot is most often found at low spots in the field or at the tail-end of irrigation runs. The fungus is a soil inhabitant that survives in the soil for long periods.

    Management

    Control is difficult, but soil management that improves drainage, such as planting high, well drained beds, and carefully irrigating to avoid prolonged saturation of the soil, will reduce chances of infection. Because drought stress also makes plants susceptible to Phytophthora, ensure an even supply of moisture without major fluctuations to help suppress disease development. If a field has a history of Phytophthora disease problems, a treatment can be applied at planting.

    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 EC) 1–2 pt 48 0
    MODE-OF-ACTION GROUP NAME (NUMBER1): Phenylamide (4)
    COMMENTS: Apply as a soil application at planting; can be preplant incorporated or applied as a soil surface spray after planting.
    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