If some of your daffodils grow poorly or fail to appear in the spring, they may have been attacked by the daffodil bulb fly, Merodon equestris. The maggot-like larvae of this pest burrow into the bulbs, eating and either weakening or destroying them. (See color photos and learn more.)
Chemical control is difficult, but some of our customers have reported success with systemic insecticides such as Bayer’s 2-in-1 Rose & Flower Care. To avoid poisoning bees and other pollinators that feed on your daffodils, please wait until after you’ve dead-headed the fading flowers before applying any insecticide.
A hot water bath can also be used to kill the larvae. Shortly after the foliage has withered, dig bulbs you know or suspect are infected and submerge them in water for at least 40 minutes at 109-111° F. Take care to avoid higher temperatures which can damage the bulbs.
Although tedious and often frustrating, the safest control is to hunt the flies in late spring, as described by Suzy Wert in The Daffodil Journal. Thanks to Suzy and the American Daffodil Society for permission to reprint her witty and expert advice.
National Bulb Fly Awareness Day was celebrated in my Indianapolis garden on Saturday, May 8. I suppose this holiday is like Arbor Day, varying with the calendar and the geographic location. But for us, the timing is right the second weekend in May. So I was out there looking for bulb flies and I wanted to alert you to some tricks for locating these voracious monsters, in this or any daffodil season.
Yes, the bulb flies do make a humming sound, but you can’t always hear it when they first hatch. It’s also impossible to hear over the noise of a lawnmower, and hard to hear over air conditioners and attic fans. Once you hear it, though, you won’t forget it, and if you have an infestation, you will hear it in your sleep! (Ask me how I know!)
Yes, they only come out on sunny days — or in sunny patches on partly cloudy days. No, it’s not true you only see them at high noon. I have seen them as early as 9:45 am and as late as 4:30 pm.
I don’t often see the fly if I am not specifically on the hunt, but I can hear him or I see his shadow and I know he’s nearby. If you’re in a hurry, pass a butterfly net or a tennis racquet over your daffodil foliage. Look for things that fly up and away. Some will be bees, wasps, hornets; but you’re looking for large flies.
The bulb fly is a fly but it’s sort of furry like a bee. It’s about 3 times the size of a housefly or twice as big as a horse fly. When it flies, it looks a little bit drunk and has been described by others as a clumsy flier. It has nothing dangling down like bees have and doesn’t have an aerodynamic shape like bees have. It will cruise very low near daffodil foliage when it’s “cruising” — looking to be seen by a potential mate or when it’s looking for a place to lay eggs. Speaking of which, I have seen the bulb fly lay eggs, so cultivating the soil to fill the holes left by daffodil foliage is immaterial — they actually drill down their rear ends when they go to lay eggs if there is no hole in the preferred spot. It is my opinion that females have decided on the clump where they will lay their eggs about four or five days before they actually lay them, and they visit the spot frequently to check things out ahead of time.
When they first hatch, and they have hatched here in Indianapolis as early as April 30, their backs are chestnut brown. Later in their season, they start losing the chestnut color and turn black. As this is happening, the hum definitely gets louder, or more pronounced, and they are most probably mating, or they’ve just mated. When they are black, females are looking for a place to drop their eggs.
No, it’s not true they prefer standard [full-size] cultivars, although it is possible they prefer laying their eggs where there is only one bulb, or maybe two, instead of a clump — hence the stories about their preferring your best bulb (the new one you planted last year). It is my opinion they actually prefer a clump of miniatures — maybe it’s a kind of delicacy in the same way that we prefer new asparagus because it’s more tender.
In my garden, bulb flies like to sun themselves on the shiny foliage of hollies, euonymus, new ivy leaves, or on hostas that are either shiny or have white edges. They also will sit on a bent daffodil leaf that is in the sun. Every year I find some on the weedy star-of-Bethlehem foliage. Also, look for them in sunny patches in dappled shade. They seem to like to dry their wings directly after hatching (and I only say this because the ones I catch are very light chestnut brown and very slow to fly, so I assume they’ve just hatched) and are an easy kill then.
One more thing I’ve noticed: if you see one in a certain spot, it will return to that spot. Go inside and leave your net by the door — you can read your email, have lunch, get the mail, start dinner, whatever you choose, and come back in fifteen minutes or half an hour later with your net at the ready, and chances are you’ll see it again.
If you see even one bulb fly, you need to be prepared for the hunt. Wear the appropriate clothing — I have found muted colors like khaki and olive are the best for hunting, but sea-foam green, soft pink, and pale yellow are also acceptable apparel. Do not wear a white T-shirt with a big red flower, or they’ll see you well before you see them. And keep the sun in your eyes so they can’t see your shadow as you’re trying to sneak up on them.
If you need to spend extended time outdoors, I advise you to have the following items:
You’ll need something constructive to do while you’re outside. You can weed, plant your annuals, check how the daffodil seed pods are ripening, decide which bulbs you want to cull from your collection, or mark where you have spaces for more bulbs — anything that will keep you in the daffodil patch(es).
If you see the bulb fly sitting still within reach of your net, come straight down over them like an overhand smash in tennis. They will fly straight up and into the net, which gives you a couple of extra seconds to bring the net closer to you, and grab the net itself with your other hand, trapping them into the very top of it.
You don’t need to smash your net over the foliage to the ground as long as you have it over the top of them, because they fly straight up before they start looking around for an open edge where the net isn’t closed off. Take the net to some hard ground and smash it with your foot while the fly is still inside the net. They are hard to catch while they are flying, but always use the same method — overhead smash — because a sideways swipe has air movement associated with it which will push the bulb fly along faster than the net can capture him, or maybe they see the net coming from the side and are able to dodge it.
Today I am ecstatic because I caught two in one net. I had only done that once before. (Small things make me happy sometimes!)
There is a same-sized bug out there, with a similar flight pattern, but it is different from the bulb fly in two ways. First, when you put a net on it, it goes down and tries to burrow — bulb flies fly straight up into the net. The other difference is, when you crush it with your foot you’ll hear that it’s hard-shelled, like a beetle. It also has little spots on it, which the bulb fly doesn’t have; but you can’t see that when it’s on the wing.
I think that’s it — time to go back on safari!