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Trouble with bulb pest

Q: I have a planting of daffodils that has been doing poorly for a couple of years. I recently dug up some of the bulbs and found that many were infested with maggots. Can you tell me what this pest is and how to control it?

George Fatula, Mount Desert Island, ME

Narcissus bulb flies can wreak havoc. The larvae of these pests work their way into the bulb, where they destroy the flower bud.

A: Becky Heath, bulb specialist and co-owner of Brent and Becky's Bulbs in Gloucester, Virginia, replies: It sounds like your bulbs are infested with the larvae of the narcissus bulb fly (Merodon equestris). This insect was introduced into this country from Europe around 1869. Adult flies are about 1⁄2 inch long, with brownish bodies; they resemble small honey bees. They attack daffodils and other members of the Amaryllis family. This pest is not common, so if you’re in doubt about whether this is actually the culprit, consult your local extension agent. Once you detect a bulb-fly problem, you must be vigilant to control it.

In spring, narcissus bulb flies lay eggs in the crown of host plants. The larvae, or maggots, hatch, work their way down into the bulb and eat it, hollowing out the center and destroying the flower bud. Infested bulbs often rot or produce weak, yellowed, grasslike foliage.

This pest is not easy to control, but there are some steps you can take to limit its numbers. If you suspect there might be a problem, dig up all of your daffodils in June, before the foliage dies. Immediately throw away any bulbs that are obviously infested and rotting. Store the remaining bulbs in a dry location with plenty of air circulation. At the end of summer, once again check each bulb for signs of the larvae; you may see a hole in the bulb, or it may have a very soft, hollow-feeling neck. There might also be a tiny, white growth (about the size of a tooth) attached to the base of the bulb. Discard all bulbs with these symptoms because they probably contain the bulb fly larvae. Replant the healthy bulbs in fall, but continue to monitor them the following spring for signs of infestation.

It may also be helpful to remove bulb foliage as soon as it dies in late spring, and then cultivate the soil around the plants. This will make it more difficult for the bulb flies to find crowns of daffodils in which to lay their eggs.

From Fine Gardening 73, pp. 96