Agriculture: Cole Crops Pest Management Guidelines

Seedcorn Maggot

  • Delia platura
  • Description of the Pest

    Seedcorn maggot larvae are legless, white, and up to 0.4 inch long. They cannot be distinguished from other Delia spp., such as cabbage maggot, without microscopic examination by a taxonomist. However, unlike cabbage maggot, seedcorn maggot does not attack plants after the seedling stage and is rarely found tunneling in larger roots. Their damage is typically restricted to cole crops that are 1 to 2 weeks old.

    Adults are dark gray flies about one-half the size of the common house fly. Females are attracted to lay eggs in moist soil that is high in organic matter. Larvae burrow beneath the surface to feed for 1 to 3 weeks on seeds and germinating seedlings. Mature larvae form oblong, brown pupae in soil.

    Seedcorn maggot can be a problem in coastal areas on broccoli and cauliflower if the weather is cool and wet. There are several generations per year. Seedcorn maggots are most prevalent during cool spring conditions, especially after wet winters. Their numbers may decline in summer.


    The larvae damage and kill germinating seeds and very small seedlings. Affected seedlings may wilt, be abnormally light green, and stunted. Once the stand is established and seedlings have developed a few leaves, seedcorn maggot is unlikely to cause economic damage.


    The key to reducing damage from seedcorn maggot is allowing plant debris and other organic matter to completely decompose before planting. Once crop seedlings emerge or right after transplanting, watch for wilting, atypically light-green plants, or reduced growth, which may indicate a seedcorn maggot infestation.

    Use primarily cultural controls to manage seedcorn maggot:

    • Disc under cover crops at least 2 weeks before planting.
    • Allow crop residue to completely decompose before planting cole crops.
    • When direct seeding, attach drag chains behind the planter to eliminate the moisture gradient from overturned soil that may attract egg-laying females to the seed row.
    • Transplant instead of direct seeding.
    • Insecticides are generally not necessary in desert areas where seedcorn maggot is not a problem. Cole crops typically grow out of seedcorn maggot damage in this region.

    In areas where seedcorn maggot damage is a problem, seed treatment or a soil-applied insecticide are effective forms of control.

    In the San Joaquin Valley, spring-planted fields with soil high in organic matter may require insecticide application. However, to avoid damage from seedcorn maggot, it is best to plant only after organic matter has decomposed.

    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 harmful to natural enemies, honey bees, and the environment are at the top of the table. When choosing a pesticide, consider information relating to air and water quality, resistance management, and the pesticide's properties and application timing. Always read the label of the product being used.
    Seed Treatment
      (NipsIt Vegetables) Label rates 12 NA
      COMMENTS: Registered for use on only broccoli seeds in California, but seed treated in and obtained from another state can be legally used in California even if the chemical is not registered on the crop in California. Contact your retail seed dealer for information and availability. Application rate per seed depends on the amount of seed planted per acre.
    Soil Application
      (Belay) 9–12 fl oz 12 21
      COMMENTS: Soil application. Highly toxic to bees for more than 5 days after an application. This product has potential to leach into groundwater where soils are permeable, particularly where the water table is shallow.
      (Capture LFR) 3.4–6.8 fl oz 12 NA
      COMMENTS: Preplant or at-plant application.
      (Durivo) 10–13 fl oz 12 30
      COMMENTS: Thiamethoxam and its metabolites (which include the neonicotinoid clothianidin) are highly toxic to bees; may pose a risk to pollinators in crops grown for seed. This product has potential to leach into groundwater where soils are permeable, particularly where the water table is shallow.
      (Verimark) 10–13.5 fl oz 4 NA
      COMMENTS: Allowed for at-plant application only (see label for more information).
      (Diazinon 50W) 4–6 lb 96 (4 days) NA
      COMMENTS: Preplant or transplant water application only (see label for more information). Not registered for use on kohlrabi, mizuna, mustard spinach, and rape greens. Avoid drift and tailwater runoff into surface waters.
    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.
    * Permit required from county agricultural commissioner for purchase or use.
    1 Rotate insecticides with a different mode-of-action group number, and do not use products with the same mode-of-action group number more than twice per season to help prevent the development of resistance. For example, the organophosphates have a group number of 1B; insecticides with a 1B group number should be alternated with insecticides that have a group number other than 1B. Mode-of-action group numbers are assigned by IRAC (Insecticide Resistance Action Committee).
    Text Updated: 12/20
    Treatment Table Updated: 12/20