Leek moth was mainly found in southern England but it is spreading north, it is not as frequently seen as the allium leaf mining fly. The caterpillars feed within the foliage and stems or bulbs of leeks, onions and related plants.
Latin name Acrolepiopsis assectella
Plants affected Leek, onion, shallot, garlic
Main symptoms White patches on leaves, with young plants rotting and dying. Small caterpillars may be seen in the plant tissues
Caused by Caterpillars of a small moth
What is leek moth?
Nearly 900 insects, including some flies, beetles, moths and sawflies create leaf mines as larvae in Britain. More information about these insects can be found at The leaf and stem mines of British flies and other insects
Damage from leek moth caterpillars appears as;
- White patches developing on the foliage where the caterpillars have eaten the internal tissues
- Tunnels in the stems of leeks and bulbs of onions, shallots and garlic
- Affected plants often develop secondary rots and young leek plants may be killed
Note that these plants can be affected in a similar manner by larvae of the allium leaf-mining fly (allium leaf-miner);
- Leek moth caterpillars are creamy-white with brown heads and small legs. They do not usually pupate within plant tissues
- Larvae of the leaf-mining fly are white, headless maggots with no legs. Cylindrical brown 3mm long pupae are likely to be found embedded in the stems and bulbs
- The female moths can be prevented from laying eggs by covering susceptible plants with insect-proof mesh. Crop rotation should also be practised to prevent potential build-up of moth populations under the mesh. The mesh should be kept in place for the entire growing season.
- Look for the white, net-like silk cocoons on the foliage and squash them
- Encourage natural enemies in gardens, predators such as ground and rove beetles are likely to consume some pupae
None of the pesticides available to home gardeners for use on leeks and onions will give effective control of leek moth.
Leek moth has two generations during the summer with larvae feeding on the plants in May to June and August to October. The second generation is the more numerous. Initially the caterpillars mine the foliage but the older larvae bore into the stems and bulbs.
When fully fed, the caterpillars are 11 mm long. They exit the plant and pupate within net-like silk cocoons that are spun on the foliage. Adult moths emerge in autumn and overwinter in sheltered places.
The Royal Horticultural Society is the UK’s leading gardening charity. We aim to enrich everyone’s life through plants, and make the UK a greener and more beautiful place.