How to Manage Pests

UC Pest Management Guidelines

Dry Beans

Seedcorn Maggot

Scientific name: Delia platura

(Reviewed 6/18, updated 6/18)

In this Guideline:


The seedcorn maggot adult is a slender, light-gray fly, about 0.2 inch (5 mm) long, resembling a small housefly. The whitish eggs are slightly curved and elongated, similar in shape to grains of rice. Slightly raised ridges run the length and width of the eggs forming tiny rectangles twice as long as wide. Larvae range from 0.2 to 0.25 inch (5–6 mm) in length. They are brownish white to whitish-yellow, cylindrical, and taper anteriorly. Pupae are small brown capsules. The seedcorn maggot is abundant during or following a wet cycle, which is primarily in spring (though this can also occur in fall on garbanzos). It is most common in fields containing high amounts of residue from previous crops or in fields where manure has been spread.


Seedcorn maggots burrow into bean seeds and prevent germination. Slow emergence and poor stand establishment are signs of seedcorn maggot activity. Where slow, spotty emergence is observed, seed should be dug up and inspected for maggot feeding. Cool soil temperatures and periods of excessive moisture delay seed germination and seedling emergence, which increase the susceptibility of bean seeds to seedcorn maggot infestation.


Cultural Control

To prevent seedcorn maggot damage:

  • Reduce the attractiveness of the field to egg-laying adults by discing or plowing under previous crop residues and weeds early in the season.
  • Plant under ideal soil and weather conditions to assure rapid seed germination and minimize the potential for seedcorn maggot damage.
  • Monitor for seedcorn maggot adults before early plantings if the bean crop will directly follow heavy cover crops or weed residue, especially during cool, wet springs.
  • Fill a yellow bowl with soapy water and place in the field.
  • Count the adult flies that fall in to the bowl every several days.
  • Do not begin planting until the numbers of adults in the bowl start to drop off.
Organically Acceptable Methods

Use cultural controls for an organically certified crop.

Treatment Decisions

Begin inspecting plants for seedcorn maggot damage when the crop emerges. If the stand is poor and emergence is sporadic, look for rotted seed in the soil. If any signs of infestation occur, use treated seed in the future.

Common name Amount per acre** REI‡ PHI‡
(Example trade name)   (hours) (days)
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
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.
  (Cruiser 5FS) 1.28 fl oz per 100 lbs seed NA NA
** See label for dilution rates.
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.


[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Dry Beans
UC ANR Publication 3446

Insects and Mites

R. F. Long, UC Cooperative Extension, Yolo County
P. B. Goodell (emeritus), UC IPM Program

Acknowledgment for contributions to Insects and Mites:
L. D. Godfrey, Entomology, UC Davis

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