How To Fight & Prevent Onion Flies

The onion fly is very similar in appearance to the common house fly, but it is a thorn in the side of every home grower. We tell you how you can effectively protect yourself against an infestation. Be curious and read on.

How do I recognize the onion fly?

Onion flies usually lay their eggs in May. The egg clutch is laid right next to the fresh shoots of the onions. After about a week, the maggots hatch and eat their way through the young onion plants. In this process, one maggot can damage several plants.

After the big feeding the maggots pupate in the soil and in summer the new generation of onion flies hatches. Up to three generations of onion flies can spoil a hobby gardener’s harvest. Often the fly is found not only on onions, but also on chives and even tulips.

Preventing an onion fly infestation – Here’s how!

We recommend installing a vegetable protection net after sowing the first plants. This provides safe and permanent protection from onion flies and other uninvited guests such as carrot flies.

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A vegetable protection net should have a mesh size of no more than 1.6mm to provide effective protection. In this case, the net completely covers the bed until just before harvest. As the plants grow, the net should be loosened a little, otherwise the bulbous plants will push the net up.

Tip: Sow the onion plants as late as possible and avoid strong-smelling manure.

Every gardener should also sow their vegetables in a different spot in the garden each year. So be creative and rotate the locations of your favorite varieties. Mixed crops in bed with carrots or pole soil effectively counteract onion fly infestations.

An insect hotel in the garden should not be missing. This will encourage beneficial insects in the garden such as spiders, beetles and ichneumon wasps, which are the natural enemy of onion flies.

Fighting onion flies

How do I get rid of onion flies once they have taken up residence in the garden? Here, approved insecticides are suitable for mixing or already ready as a spray bottle.

Biological sprays against onion flies

  • Tansy tea is suitable as a natural remedy against onion flies. Collect the plants and pour hot water over them. After 24h, squeeze out the tar residue and apply to the appropriate onion plants with a squirt of dishwashing liquid.
  • The stinging nettle as a wonder weapon in the garden also helps here. Make a nettle decoction. Mix thereby in the ratio 1:10 – 100gr fresh nettle with a liter of water mix. Stir the fresh broth several times a day until the first bubbles rise to the surface. Then the broth is ready and can be applied to the onion plants with a watering can or spray bottle.


An infestation of onion flies is very annoying. The infestation can be effectively prevented with protective nets. If it is already too late, then a nettle broth, tansy tea or even chemical means of control will help. We wish you good luck and a successful harvest.

Frequently Asked Questions (FAQ)

1. When is the onion fly active?

The onion fly is very similar in appearance to the house fly. The first generation usually appears in late April to May.

2. What can be done against the onion fly?

The most effective prevention is with vegetable protection nets. If an infestation has already occurred, useful home remedies can help. Learn more here.

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