How to Tell You Have Allium Leaf Miner
The pest only attacks members of the onion family. Leeks, chives, garlic, shallots and onions are very much at risk.
The track marks on the leaves indicate eggs are being laid. Sometimes the leaves will show tracks from the tunnels (galleries) eaten by the maggot. The leaves will curl and collapse.
Maggots can be found inside vertical tunnels inside the leaves and flesh of the plant. Small brown pupae are found at the base of the tunnels near the surface but inside the plant. The tracks may be easier to spot.
Control of the Allium Leaf Miner
The only practical control is to cover the crop. Danger periods are March to June and Sept to Nov. The Hut sells Debris netting and is a proven barrier against Leek Moth. It comes 2 metre wide and costs £1.60 per metre.
If the infestation is detected in the crop, affected plants should be uprooted and burned. Don’t compost infested plants, the pupae will still be able to hatch spreading the infection.
Search online for Alys Fowler (Gardeners World) for a different approach.