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Onion Maggot Control

The onion maggot is the most significant pest of onions in our area. The problem is so extensive that in many areas onions cannot be grown without insecticidal treatment.

The adult of the onion maggot is a small fly about half the size of a housefly. The female fly lays her eggs at ground level on the base of the stalk of the emerging onion early in the spring. The egg hatches into the maggot, which is the destructive stage. The maggot burrows into the onion bulb which causes the plant to become flabby and begin to yellow. Small onion bulbs may become completely mined out by maggot feeding. In large bulbs the maggots eat out cavities which contribute to later rotting in storage.

Onion maggot control should be applied at planting time. An in-furrow application of Dursban Lawn and Garden Insect Control is an effective onion maggot control technique. A second lay-by treatment can be applied later in the season to protect larger bulbs that are left to mature for dry winter onions. For an organic method of control, sprinkle diatomaceous earth around transplants which you want to protect. The fine fossilized shell material has microscopic sharp edges that pierce soft bodies and causes them to dehydrate. Apply after a light rain for better effectiveness.

Additional information on this topic is included in the Extension bulletin E-331, "Garden Insect Control Guide," which is available at your county office of the NDSU Extension Service.

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