CORNELL COOPERATIVE

EXTENSION OF ONEIDA COUNTY 121 Second Street Oriskany, NY 13424-9799 (315) 736-3394 or (315) 337-2531 FAX: (315) 736-2580 Maggots

Damage The onion maggot ( antiqua) is one of the most destructive pest of and related plants. The first noticeable damage from onion maggot injury is the wilting of foliage. The plant eventu- ally becomes flaccid and collapses. This type of damage is very noticeable when the plants are seed- lings. Light infestations may not kill onions but may make them more susceptible to rots. Onions of all sizes may be attacked, especially in the fall, when cooler weather fa- vors the maggots activity. Damaged onions are not marketable and will rot in storage causing other onions to rot. Once onion maggots infest an area, they seem to be a problem every year. White onion varieties are more susceptible to attack than other varieties.

Life cycle The adults of the onion maggot are , which resemble but are smaller 1/3”. The flies are grayish black in color. In NY State there are three overlapping broods which occur. On Long Island the first adults appear in spring, usually around May 1st. This brood is the most damaging to the crop. A week to 10 days after emerging, mating occurs and the female lays eggs. These eggs are laid in the young leaves or necks of the onion plant at or in the soil near the plant. De- pending on food, each female can lay several hundred eggs. Eggs hatch in 2-3 days.

The larvae 1/4” (maggots) are legless and creamy white in color. Usu- ally these maggots enter at the base of the onion plant and feed on the tissues with their hooked mouthparts. Maggots will leave filled seed- lings and migrate to a live plant. A single maggot can kill 20 small seedlings. After going through three larval stages (2-4 weeks) the maggot leaves the onion and pupate in the soil.

The pupae are chestnut brown in color. The onion maggot over-winters in this stage. Other broods spend 2-4 weeks in this stage during the season.

Helping You Put Knowledge to Work

Cornell Cooperative Extension provides equal program and employment opportunities. NYS College of Agriculture and Life Sciences, NYS College of Human Ecology, and NYS College of Veterinary Medicine at Cornell University, Cooperative Extension associations, county governing bodies, and U.S. Department of Agriculture, cooperating. Management The onion maggot has many natural enemies such as ground beetles, birds, parasitic wasps, nema- todes and a parasitic fungus that is most effective in cool, wet weather. There seem to be no resis- tant varieties at this time except for a Japanese bunching onion that, at times, shows resistance, or at least tolerance.

Rotation as a method of maggot control is not always practical for the home gardener, but controlling wild onions should help. Volunteer onions and may be a source of infestations. The onions should be removed and the wastes burned and not plowed into the soil. Highly organic soil may be more attractive to the flies.

If crop rotation is not possible, remove infested soil and replace with fresh soil.

Authorities differ as to whether fall plowing is advisable. Some say plowing exposes the pupa to predation and dehydration; others claim it only protects the pests.

Controlling the spring infestation is most important because small or new plants are most easily damaged. Killing flies or maggots in the spring helps lower populations in the fall.

There are no current insecticides recommendations for home- owner use to control this pest

Sources: http://pmo.umext.maine.edu/factsht/Onionm.htm

http://www.nysaes.cornell.edu/ent/factsheets/damage/om_onions. html

Prepared by: Thomas Kowalsick, Extension Educator, Cornell Coop- erative Extension-Suffolk County. Reference: The Onion Maggotand its control in NY, P.R. Ellis and CJ Eckenrode, NYS Experiment Sta- tion at Geneva.

Management recommendations obtained from Part 1 Pest Manage- ment around the Home Cultural Methods, 7/00, Miscellaneous Bulle- tin s74-I a Cornell Cooperative Extension Publication

This publication may contain pesticide recommendations. Changes in pesticide regulations occur constantly, some materials mentioned may no longer be available, and some uses may no longer be legal. All pesticides distributed, sold, and/or applied in New York State must be registered with the New York State Department of Environmental Conservation (DEC). Questions concerning the legality and/or registration status for pesticide use in New York State should be directed to the appropriate Cornell Cooperative Extension Specialist or your regional DEC office. READ THE LABEL BEFORE APPLYING ANY PESTICIDE.