How to Manage Pests

UC Pest Management Guidelines


Seedcorn Maggot

Scientific Name: Delia platura

(Reviewed 12/09, updated 6/12)

In this Guideline:


The seedcorn maggot is the larva of a small, light gray fly that is about 0.15 inch (4 mm) long. The whitish, legless maggots are about 0.3 inch (8 mm) long and attack the planted seed of a number of crops during the winter and early spring months, particularly if there is a cold period that prevents quick germination of the seed. Maggots may overwinter in the soil or hatch from eggs laid in spring.


The maggot attacks germinating seeds or transplants, but is only a pest early in the season before the soil warms up. Little damage is likely to occur once favorable growing conditions set in. Seedcorn maggots are particularly damaging when residues of the previous crop have not thoroughly decayed before planting cucurbits.


A preventive seed treatment is particularly important when planting in no-till, conservation-till, and when planting through cover crops to prevent seed corn maggot damage. Additionally, good field sanitation, and production measures that ensure rapid seed germination are important in controlling seed corn maggots.

Cultural Control

Fields with moist, heavy-textured soil usually have the worst problem with this pest. To reduce attractiveness of the field to egg-laying adults, disc or plow early in the season to incorporate residues from the previous crop and allow time for residues to completely decompose before planting. Destroy weed growth. Avoid planting cucurbits after root crops or cole crops, including cabbage, cauliflower, broccoli, and Brussels sprouts, and after fall tomatoes. Assure rapid seed germination by planting in moist soil and not too deep (1.25 to 1.5 inch depth is ideal for melons) when weather conditions are ideal. The longer the germination the greater the risk of infestation. Late-season planting may avoid the early season infestation of this pest.

Organically Acceptable Methods

Cultural controls are acceptable to use in an organically certified crop.

Monitoring and Treatment Decisions

A preventive seed treatment is the best method of control.

Common name Amount per acre R.E.I.‡ P.H.I.‡
(example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
When choosing a pesticide, consider information relating to water quality and impact on natural enemies and honey bees. Not all registered pesticides are listed. Always read the label of the product being used.
CAUTION: Do not use treated seed for human consumption, for livestock or poultry, or for oil purposes. Label treated seed as follows: TREATED SEED. DO NOT USE FOR FOOD, FEED, OR OIL.
  (AG 500) 3–4 qt 3 days 3
  COMMENTS: For use in melon fields only; broadcast just before planting and incorporate. Avid drift and tail water runoff into surface waters.
  (Vapam) 75 gal see label NA
  COMMENTS: Wait at least 14 days after fumigation before planting. Fumigants such as metam sodium are a source of volatile organic compounds (VOCs) but are minimally reactive with other air contaminants that form ozone. Fumigate only as a last resort when other management strategies have not been successful or are not available.
Restricted entry interval (R.E.I.) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Preharvest interval (P.H.I.) is the number of days from treatment to harvest. In some cases the REI exceeds the PHI. The longer of two intervals is the minimum time that must elapse before harvest.
* Permit required from county agricultural commissioner for purchase or use.
1 Rotate chemicals 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; chemicals with a 1B Group number should be alternated with chemicals that have a Group number other than 1B. Mode of action Group numbers are assigned by IRAC (Insecticide Resistance Action Committee). For additional information, see their Web site at
NA Not applicable.



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Cucurbits
UC ANR Publication 3445

Insects and Mites

  • E. T. Natwick, UC Cooperative Extension, Imperial County
  • J. J. Stapleton, UC IPM Program, Kearney Agricultultural Center, Parlier
  • C. S. Stoddard, UC Cooperative Extension, Merced & Madera counties
Acknowledgment for contributions to Insects and Mites:
  • R. L. Coviello, UC Cooperative Extension, Fresno County
  • L. D. Godfrey, Entomology, UC Davis
  • C. B. Fouche, UC Cooperative Extension, San Joaquin County
  • C. G. Summers, Entomology, UC Davis/Kearney Agricultural Center, Parlier
  • J. B. LeBoeuf, AgriData Sensing, Inc., Fresno
  • M. Murray, UC Cooperative Extension, Colusa/Glenn counties

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Statewide IPM Program, Agriculture and Natural Resources, University of California
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