Garden pest
Onion maggot
Seedlings wilt; white maggots in the bulb base. Float a row cover over the row; rotate beds each year.
Onion maggot is in its active season now — scout your plants this week.
How to identify onion maggot
The adult is a slender gray fly a little smaller than a housefly, easy to overlook among the onions. You'll rarely notice it before the damage shows.
The larva is a legless white maggot that tunnels into the base of the bulb. You find it by pulling a wilting, yellowing seedling and splitting the base open.
Attacks: Onions, Garlic, Leeks
Life cycle: Flies emerge in spring and lay eggs at the base of onion-family plants or in nearby soil; the maggots bore into the developing bulb. Two to three overlapping generations run through the season, with the first the most damaging to young plants.
Signs of onion maggot
What you actually see on the plant — usually before you spot the pest itself.
- Seedlings that wilt, yellow, and collapse in patches
- White legless maggots tunneling in the base of the bulb
- Soft, rotting bulbs where secondary rot follows the feeding
- Gaps in the row as young plants die out
Organic control, least-toxic first
Start at the top and only move down if you need to. Physical and cultural fixes come before any spray.
- Float a row cover over the row
Fine insect netting or a floating row cover laid over the bed from planting keeps the egg-laying flies off the crop. Seal the edges to the soil so the low-flying adults can't slip underneath.
- Rotate the bed every year
Pupae overwinter in the soil, so moving the onion-family crop to a new spot each year, as far from last year's bed as you can, keeps the emerging flies away from fresh plants.
- Pull and remove culls and rotting bulbs
Damaged and rotting bulbs and thinnings give off the smell that draws egg-laying flies. Pull them out and take them away from the garden rather than leaving them in or beside the row.
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One rule for any product you spray: follow the label. The label is the law, and it is the tested, safe rate for your plants — homemade mixes and dish-soap sprays are not, and can scorch foliage.
Prevent it next season
- Don't plant onions into fresh manure — high-organic, rotting soils are far worse for onion maggot
- Rotate onion-family crops on a multi-year cycle and avoid replanting where they grew last year
- Remove culls, thinnings, and rotting bulbs so they don't attract flies to lay eggs
- Cover early plantings, which take the hardest hit in cool wet springs
Questions about onion maggot
Why are my onion seedlings wilting and dying?+
Likely onion maggots. Split the base of a wilted plant and look for white maggots tunneling into the bulb. The fix is a floating row cover to block the flies plus rotating the bed each year.
What makes onion maggot worse?+
Cool, wet springs and high-organic soils, especially beds dressed with fresh manure. Rotting culls left in the row also draw egg-laying flies, so pull and remove them.
Can I spray for onion maggot?+
Sprays do little because the maggots feed hidden inside the bulb base. Exclusion with a sealed row cover, yearly rotation, and removing culls do far more than any spray.
Plan a garden that fights back
Healthy, well-spaced plants shrug off pests that flatten a crowded bed. PlotToTable sizes your beds, spaces every crop, and flags the pests that hit what you grow.