Allium Leaf Miner
Pest · Commonly affects: Leek, Onion, Garlic, Spring onion, Shallot, Chives, Welsh onion
Allium leaf miner is a troublesome pest of leeks, onions and garlic, particularly where crops are grown without protective covers. The larvae tunnel inside leaves and stems, making vegetables unattractive and allowing decay to enter. It has two main adult flight periods in spring and autumn, so timely exclusion is more effective than trying to deal with an infestation later.
How to identify it
Adult flies are small, grey-brown insects about 3 mm long and are seldom seen. Early signs include rows of tiny pale punctures made by feeding females on leaf tips. Creamy-white larvae, up to about 8 mm, make linear tunnels within leaves; later, brown, barrel-shaped pupae about 3-4 mm long may be visible in damaged tissue. Leeks may show distorted leaves, soft patches and rust-coloured lines along the shafts.
Damage
Larval tunnels weaken leaves and can extend into leek shafts, onion bulbs and garlic stems. Damaged tissue becomes more prone to rotting, particularly in wet weather or storage. Leeks may be distorted or split, and onions can fail to size up. An affected crop may remain edible after careful trimming, but badly tunneled plants often deteriorate quickly.
Prevention
Cover alliums with fine mesh or horticultural fleece before the spring flight and again before the autumn flight, keeping edges fully sealed. Use a support frame where possible so leaves do not press tightly against the cover. Rotate crops between beds and remove volunteer onions and leeks. Start plants in a protected area, plant healthy modules, and avoid moving infested leaves or seedlings to another part of the plot.
How to manage it
Remove and dispose of visibly mined plants, pupae and crop debris promptly; do not add infested material to home compost. Peel back damaged outer leek leaves when harvesting and use sound plants without delay. Keep covers in place for the relevant flight period, repairing gaps immediately. After harvest, lift all remaining alliums and clear the bed thoroughly, then avoid growing another allium crop there in the following season.
Allium Leaf Miner: frequently asked questions
How do I identify allium leaf miner?
Adult flies are small, grey-brown insects about 3 mm long and are seldom seen.
How do I prevent allium leaf miner?
Cover alliums with fine mesh or horticultural fleece before the spring flight and again before the autumn flight, keeping edges fully sealed.
How do I get rid of allium leaf miner?
Remove and dispose of visibly mined plants, pupae and crop debris promptly; do not add infested material to home compost.
General guidance for UK home gardens and allotments, focused on prevention and non-chemical control. For a confirmed diagnosis, the RHS or a local garden centre can help. Page updated 19 Sep 2026.