Leek moth caterpillar
Look for a small creamy-green caterpillar with a distinct brown head and legs, feeding in white leaf patches or tunnels within stems and bulbs.
Pest guidesDiagnose damaged leeks before acting
Leek moth or allium leaf miner? How to tell the damage apart
Both pests tunnel into alliums and invite secondary rot, but the occupant gives the strongest answer: a legged caterpillar with a brown head suggests leek moth; a legless white maggot or brown pupa points to allium leaf miner.
Start with the quick check ↓Quick check
What to inspect now
Open a damaged leaf over a tray. Look for the larva or pupa, then compare its body, head and legs rather than diagnosing from rot alone.
- Main timing
- Leek moth: mainly April–October. Allium leaf miner: March–June and September–November, with peak adult activity around March–April and September–November.
- Plants affected
- Leeks, onions, shallots, garlic and chives.
Identification
Signs that narrow it down
Allium leaf-miner maggot
Look for a white, headless-looking, legless maggot or a small cylindrical brown pupa embedded in the stem or bulb.
Adult leaf-miner feeding marks
Neat rows of pale dots on leaves can reveal adult feeding before larval damage becomes obvious. Spring foliage may twist or distort.
Secondary rot
Either pest can open tissue to bacterial and fungal infection. Rot identifies urgency, not the pest by itself.
If you confirm it
Useful action, in order
Start with the least disruptive step that protects the crop. The presence of a pest does not automatically justify treatment.
- 1
Remove badly damaged tissue
Take severely affected plants or leaves out of the crop before larvae complete development. Do not leave infested material beside the bed.
- 2
Cover during adult activity
Use fine insect-proof mesh with sealed edges before eggs are laid. Ordinary butterfly netting may not exclude small leaf-mining flies.
- 3
Check remaining plants
Inspect neighbouring alliums because damage is often hidden inside apparently sound outer leaves.
Next crop
Reduce the chance of a repeat
Protect the full seasonal window
Allium leaf miner has spring and autumn generations, while leek moth may remain active through summer. Choose cover timing for the pest present locally.
Rotate covered alliums
Pupae may remain in old crop ground. Mesh over the same place can trap emerging adults with the next crop.
Clean up carefully
Remove harvested debris that contains larvae or pupae while retaining unrelated garden habitat elsewhere.
Common questions
Practical answers
What is the easiest way to tell leek moth from allium leaf miner?
Find the immature insect. Leek moth has a caterpillar with a brown head and legs; allium leaf miner has a legless pale maggot and later a small brown cylindrical pupa.
Why are my leeks rotting from the centre?
Tunnelling by either pest can allow secondary bacterial or fungal rot. Split the stem and inspect for caterpillars, maggots or pupae.
Will butterfly netting stop allium leaf miner?
The fly is small, so use insect-proof mesh specified for leaf miners and seal all edges rather than relying on coarse bird or butterfly netting.
Sources and scope
Evidence behind this guide
SowNext summarises identification, timing and lower-impact management for UK home food growing. Local populations and protected conditions can differ, so confirm the organism before acting.