Onion Root Maggot

Delia antiqua

Onion Fly Maggot Control

The adult Onion Root Maggot resembles a small house fly. It is hump-backed, grayish brown with a slender body and long legs. Their brown pupae over-winter in the soil and adults emerge in spring. There are 3 generations of this pest each year. Eggs are deposited in leaf axles or in the soil near the base of the plant. The eggs thrive when the conditions are cool and moist. Upon hatching, larvae crawl down the plant and feed for 2 to 3 weeks.

It is the larval stage that cause harm. The white larvae are slightly over 1/4 inch when full grown. They are blunt on the rear end and tapered to a point at the front end. The Onion Maggot tunnels into onion bulbs, which may turn yellow and die before maturity. The maggot often will move from plant to plant, thus damaging several bulbs and thinning stands of young onions.

This pest is a serious pest of onions but rarely attacks other vegetable crops although they will move to carrots, parsnips, garlic and leeks if necessary to survive. Methods of control include:

For control products and more information please see our Borer Control page.

Photo courtesy of: Cornell University, Pests in the Northeastern United States.