How to Manage Pests

UC Pest Management Guidelines

Onion and Garlic


Scientific name: Liriomyza spp.

(Reviewed 1/07, updated 5/10, pesticides updated 6/16)

In this Guideline:


Adults are small black and yellow flies. Females puncture the leaf to feed on plant sap and to lay eggs within the leaf tissue. Eggs hatch within 2 to 4 days and the small white to yellow larvae tunnel within the leaf tissue. Larger larvae may feed inside the hollow leaves of onions or garlic, but still produce the characteristic "mines" visible from the outside of the leaf. Larvae exit the leaf upon completion of their development and pupate in the soil or in the leaf axils on plants. Many generations occur each year.


Damage caused by leafminers is primarily cosmetic in green bunching onions; contamination by pupae and larvae, however, is a problem. Damage in dry onions and garlic is of little concern unless populations become so high as to prematurely kill foliage.


Biological Control

Natural enemies, especially parasitic wasps, are commonly found reducing leafminer numbers. These parasitic wasps are very susceptible to insecticide sprays, however, and may not be important in fields where insecticides have been used.

Cultural Control

Leafminers attack a wide variety of crops in coastal California. Close proximity to crops such as lettuce, celery, or spinach will increase the potential for damage by leafminers in onions. It is also important that fields being planted to onions that were previously in one of these susceptible crops be worked thoroughly and that sufficient time be allowed to pass before planting into these fields to allow pupae in the soil to emerge.

Organically Acceptable Methods

Biological controls are often effective in controlling this pest in organically grown onion and garlic crops. Supplemental or inundative releases of parasites are rarely economically justified. Cultural controls as described above are critical. Azadiractin products are allowed.

Monitoring and Management Decisions

There is no established threshold for leafminer in onions. Because large populations of adults do not always lead to large larval populations, make your management decisions based on the level of larval infestations on the plants.

Common name Amount per acre REI‡ PHI‡
(Example trade name)   (hours) (days)

Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
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. Not all registered pesticides are listed. Always read the label of the product being used.
  (Trigard) 2.66 oz 12 7
  COMMENTS: For use on onion and garlic. Do not make more than six applications per crop.
  (Ambush)* 6.4–19.2 oz 12 1
  COMMENTS: For use on onion and garlic. Do not apply more than 2 lb a.i./acre per season. May cause secondary outbreaks of spider mites.
  (Mustang)* 2.4–4.3 fl oz 12 7
  COMMENTS: For use on onion and garlic. May cause secondary outbreaks of spider mites.
  (Neemix 4.5) Label rates 4 0
  COMMENTS: For use on onion and garlic. A restricted use pesticide in an organically certified crop.
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 the harvest may 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.
* Permit required from county agricultural commissioner for purchase or use.
# Acceptable for use on organically grown produce.
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 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 (un = unknown or uncertain mode of action) are assigned by IRAC (Insecticide Resistance Action Committee).



[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Onion and Garlic
UC ANR Publication 3453

Insects and Mites

S. Orloff, UC Cooperative Extension, Siskiyou County
E.T. Natwick, UC Cooperative Extension, Imperial County
L. D. Godfrey, Entomology, UC Davis
S. K. Dara, UC Cooperative Extension, Santa Barbara County

Acknowledgment for contributions to Insects and Mites:
W. E. Chaney, UC Cooperative Extension, Monterey County
R. L. Coviello, UC Cooperative Extension, Fresno County
G. J. Poole, UC Cooperative Extension, Los Angeles County

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