Skip to content
growing.guide
Menu

Onion fly

Onion fly maggots feed in the bulbs of onions, garlic and leeks. Young plants yellow, wilt and pull away easily, and bulbs rot. Allium leaf miner is a related pest that tunnels leaves and stems.

Pests
A young onion with yellow, collapsing leaves
A young onion with yellow, collapsing leaves

What it looks like

The plant collapses from below.

  • Young onions flop and yellow.
    Yellow, drooping leaves Young onions flop and yellow.
  • They come away easily when tugged.
    Loose plants They come away easily when tugged.
  • White maggots in rotting bulb tissue.
    Maggots in the bulb White maggots in rotting bulb tissue.
  • Allium leaf miner leaves lines of white dots and tunnels.
    Tunnels in stems Allium leaf miner leaves lines of white dots and tunnels.

How to confirm it

Lift a failing plant.

  1. Look inside the bulb

    Maggots and rot confirm it.

  2. Check neighbours

    Several plants in a row affected.

  3. Look for dots

    Rows of white dots on leaves mean allium leaf miner.

What to do

Protect and clear.

  1. Cover the crop

    Use fine mesh over onions and garlic.

  2. Remove affected plants

    Lift and destroy infested plants.

  3. Grow sets

    Onion sets are less attractive than seedlings.

  4. Avoid damage

    Do not bruise leaves when weeding; the smell attracts flies.

Prevent it next time

  • Rotate alliums.
  • Cover crops during the fly's egg-laying periods.
  • Clear debris after harvest.

What not to do

Do not compost infested bulbs.

In the growing guides

Where the guides mention it, with plant-specific advice.

Sources

  1. Onion fly, Royal Horticultural Society
  2. Allium leaf miner, Royal Horticultural Society