Onion Maggots

Onion maggots are very small measuring around 9mm. The adult is a fly that is about 9mm long, greyish coloured with large wings. 

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Onion Maggot-Later’s, Maggots & Pupae-Jack Kelly Clark

Onion maggots are very small measuring around 9mm. The adult is a fly that is about 9mm long, greyish coloured with large wings. They lay their eggs around the base of onions and garlic in the spring after they emerge for overwintering pupae. Eggs hatch and the larva feed on the onions. The maggots can feed for up to 3 weeks before they become a soft brown pupae.

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Onion Maggot Flies-Manitoba Agriculture, Fly, Larva and Pupae-University of Maine

They are found in cooler damper areas. Cool coastal climates are where they are prevalent. You can find these guys near dandelions and edge weeds around the garden.

Plants turn yellow and the maggots hollow out the whole onion if given a chance. Large bulbs will rot. Destroy all affected plants.

Maggot damage on onions-University of California

1) Sticky Traps
Yellow sticky traps will capture the flies in the spring. Tanglefoot is a good organic substance that can be safely sprayed or spread on stems and catches anything that climbs up.
2) Plan Your Planting Times
When planting onions and garlic in cooler climates, like the Pacific Northwest, it would be best to either plant in february when the flies are not present or wait until after the spring hatch of the flies. (mid-May) If you live in the Pacific Northwest there are several types of green onions that will thrive in the winter.
3) Rotate Your Crops
Pupae overwinter in the ground where the affected plants are, so rotating will give you a head start on controlling these guys. Clean up all garden debris before you close your garden for the winter.
4) Wood Ashes
Sprinkle wood ashes and cayenne pepper around the plants to discourage egg laying. Be very careful what ashes you use. Ashes from your wood stove or fireplace are the best choice. Be sure that wood has not been treated with chemicalss and that nothing other than newspaper was also burned. Coated papers, cig butts, and other things tossed in the fire can contaminate your crops. Know where your ashes came from before you apply.
5) Build Raised Beds
These guys love poorly drained soil, so a good idea would be to plant your onions and or garlic in raised beds.

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  1. Laara says

    I live in the cold northern part of B.C. Canada, and each year I have had onion maggots in my gardens also. One year I put tea leaves
    in the hole -about 4heaping tbsp.- before planting my onions and also in the radishs, I forget where I learned this, but man, this year proves that it really works! I now have onions that are half
    way mature, but are succuming to onion maggots because I never used the tea leave, sooo, tonite I am going to water them with a good stong mix of STEEPED tea leaves and see it that helps, I think it will save the rest of my onion transplants.
    Also, I have learned the best way to deal with fruit flies, is to set out a small amount of vinegar in an 8oz glass and empty it ever
    second day. Good luck youall

  2. Matt says

    The most informative article I’ve found on this yet, short of the Rutger’s FS278 Fact Sheet on this subject. I find I oddly relate, because I live in Southern California and recently had a fruit fly incident.
    A few days ago I noticed a few small black poorly flying flys. They were always gathered around my kitchen or bathroom sink. I was confused since both are fairly clean. Last night I realized that there was an old onion in an open bag on top of my fridge that my girlfriend left there.

    I had found the source of my swarm’s breeding, and rather fortuitously since the bag was half closed it served as a decent trap. I was able to quickly grab it and tie the end off before any more flys could get out. There could have been over 100 in there. about half the red onion was turned into fermenting liquid.

    I’m a bit paranoid about having had a nest in my place, and am worried they could start breeding inside my disposals or clogged pipes. I first noticed the flies hanging around my kitchen sink and wonder if they might be breeding right now…. Is it true they lay upto 500 eggs at a time? Or would fruit flies leave since I don’t have a single piece of fruit, juice, vinegar or wine open? I’ll probably play it safe and snake out all my drains this weekend anyways just curious.

    Thanks for the great content

  3. Jack Laub says

    When I lived in northern Utah I was told that the pests in my radishes were onion maggots, and they looked very much like those pictured above. Does this make sense? Since I moved to the hot deserts of Arizona I have not had any problem with them in either my onions or radishes. Do they not exist in this climate?

  4. Cahri says

    Not really. If you let your onions go to seed and flower then I suppose pollination would be beneficial.

  5. Cahri says

    This depends on your area. If you are still awaiting summer heat then you should leave them on for a few more weeks. These guys are finished when the heat turns on. Remember though that you need to remove the covers so that your pollinaters do thier jobs.

  6. Sandy Forrest says

    I have covered my onions with a garden fabric and it has worked very well.I am hearing that the flies lay their eggs from spring until fall.Is this true??I would like to soon take the fabric off.thankyou.

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