Onion & garlic maggot
A hidden grub that tunnels into the bulb underground — the first sign is often a wilting plant or a rotten bulb, not the pest itself.
- Pest type
- Fly maggot (soil)
- Attacks
- Bulb base & roots
- Worst in
- Onion/garlic grown year after year
- Main risk
- Hidden bulb rot
Overview
Onion and garlic maggot is the grub (young stage) of a small fly. The fly lays eggs in the soil near young plants or in cracks around the bulb, and the grubs that hatch tunnel straight into the base of the bulb and the roots.
Because the damage happens underground, a farmer usually notices it only when plants wilt or yellow for no clear reason, or when bulbs are found rotten at harvest or in storage. Once the maggot opens the bulb, bacteria and fungi move in and finish the damage, so a mild maggot attack can turn into a bad rot problem.
How to identify it
- Plants wilt, turn yellow or look stunted for no obvious reason, even when watered properly.
- Pull up a suspect plant and check the bulb base and roots for small, white, legless grubs, or tunnels and soft, rotten tissue.
- At harvest or in storage, some bulbs turn soft and rotten from the base upward, sometimes with a bad smell from secondary rot.
- Worst where onion or garlic is grown in the same field season after season, or in cool, wet soil.
The damage it does
- Maggots tunnel into the bulb base and roots, weakening or killing young plants outright.
- The tunnels let in bacteria and fungi, so a plant that survives the maggot often still loses the bulb to rot.
- Damaged bulbs rot further in storage, turning a small field problem into a bigger loss after harvest.
- Losses are usually patchy in the field but can be severe in a badly affected patch.
When to act
- Check wilting or yellowing plants early by pulling one or two up to look at the bulb base, rather than waiting to see if they recover.
- Inspect bulbs carefully at harvest and again before storing, and keep only firm, healthy bulbs for store or for seed.
- Act on the field problem before the next onion or garlic crop, since the maggot builds up in soil that keeps growing the same crop.
Organic & cultural control
- Rotate out of onion and garlic for at least a season — this breaks the maggot’s life cycle in the soil, which is the single most effective step.
- Remove and destroy culled, damaged or rotten bulbs at harvest instead of leaving them in or near the field, since they let the pest carry over.
- Avoid waterlogged, poorly drained soil, which favours both the maggot and the bulb rots that follow it.
- Use healthy, clean planting material (sets or cloves) and avoid saving visibly damaged bulbs for the next planting.
Chemical control
- A chlorpyrifos soil drench at the base of affected plants can help where the maggot is actively spreading across the field.
- Soil or seed-furrow treatment at planting is more effective than a later spray, since the pest lives and feeds underground out of reach of foliar sprays.
- Confirm the current recommendation and dose for your area with your local KVK before spraying.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My onion plants are wilting even though I am watering them properly. What is wrong?
Pull a wilting plant and check the bulb base for small white grubs or tunnels — that is the classic sign of onion maggot. It attacks underground, so the first visible clue is often a wilting plant with no obvious cause above ground.
I found rotten bulbs at harvest. Could this be the same pest?
Yes — maggot tunnels open the bulb to bacteria and fungi, so what looks like plain bulb rot at harvest or in storage often started as maggot damage weeks earlier. Sort out and destroy any soft or rotten bulbs rather than storing them.
How do I stop it coming back next season?
Rotate away from onion and garlic for at least a season, destroy damaged bulbs instead of leaving them near the field, and avoid waterlogged soil. These steps break the pest’s life cycle far better than a spray after the damage is already done.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.