Leek Moth is a minor pest that affects leeks, onions in Scotland. Here is what it looks like, how to spot the damage, and which controls have been tested.
What does it look like?
Adults: Small, inconspicuous brown moths, 5-6mm.
Caterpillars: Creamy-white with brown heads and small legs, reaching 11mm when fully grown.
Is this pest active now?
May to June: First generation
August to October: Second generation, the more numerous
These are UK-generic timings. Scottish onset may differ. Use the Frost Date Calculator to adjust for your region.
Symptoms
White patches on foliage where caterpillars consume the internal tissues; tunnels in stems and bulbs; secondary rots developing; and young plants sometimes killed outright.
Life cycle
Two generations a year, with larvae feeding on plants in May to June and August to October. The second generation is the more numerous. Caterpillars mine foliage before boring into stems and bulbs, pupate in silk cocoons on the foliage, and adult moths overwinter in sheltered locations.
Why this matters in Scotland
This is exactly the localisation the site exists for. A Scottish gardener reading a UK-generic pest guide has no way to know whether leek moth is a real risk in Fife or a southern English problem they will never meet. The guidance places it 'mainly in southern England' and spreading north. The honest Scottish answer is: probably not yet yours, watch for it, and here is what it looks like if it arrives.
Controls: what actually works
Every method below is graded by evidence, not by how often it gets repeated. Where a claim has been tested and failed, we say so plainly.
Insect-proof mesh covering plants throughout the growing season
Cover with insect-proof mesh for the growing season. Crop rotation is essential alongside it: mesh laid over ground that already holds overwintering moths traps them in with the crop.
Exclusion by mesh is the recurring answer for insect pests generally, the same principle behind the carrot fly and cabbage caterpillar controls.
Encourage natural predators — ground and rove beetles
Search for and crush the white silk cocoons on foliage
Frequently asked questions
What should I do first if I find leek moth in my garden?
Start with insect-proof mesh covering plants throughout the growing season. After that, encourage natural predators — ground and rove beetles. The full list of evidenced controls is above, each graded by how much evidence supports it.
Will leek moth kill my plants?
They rarely kill established plants. The damage is usually cosmetic on outer leaves, and natural predators often bring numbers under control without you doing anything.
When are leek moth most active in Scotland?
Check the seasonal activity section above. Scottish timings can run a few weeks behind the UK-generic figures.
Sources
1 source, recorded with what each was used for
- RHS1: adult and caterpillar identification, affected alliums, damage, two generations with May-June and August-October timings, overwintering, southern England distribution and northward spread, comparison with allium leaf mining fly, mesh with rotation, ground and rove beetles, crushing cocoons