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The allium leaf mining fly was first detected in Britain in 2002, since when it has spread and become a problem for allium growers in much of England and parts of Wales. The larvae bore into the stems and bulbs of leeks, onions, chives and garlic with devastating consequences. Affected plants often develop secondary infections and rot.
Allium leaf miner (Phytomyza gymnostoma) on leek (Allium porrum)
Allium leaf miner can be a problem on many common crops: leeks, onion, chives, shallot and garlic. The initial damage is done by the maggots, but secondary fungal and bacterial infections often cause the most noticeable rotting.
Infestations are initiated by the adult fly:
Next seen is damage from the maggots:
But perhaps the most obvious signs of a problem appear when rotting sets in:
Plants can be protected by covering them with horticultural fleece, or an insect-proof mesh such as Ultra-Fine Enviromesh, at times when the adult flies are active and laying eggs (March to April and October to November). Crop rotation must be used, as adult flies might emerge from pupae underneath the covering if susceptible plants are grown in the same piece of ground in successive years.
None of the pesticides available to home gardeners for use on leeks, onions and allied plants is likely to give control of allium leaf miner.
Allium leaf miner has two generations a year:
The maggots bore into the foliage, stems or bulbs of their host plants and, after a couple of weeks, are fully fed and ready to turn into brown pupae. Pupation takes place mainly within the stems and bulbs during summer and winter but some pupae may end up in the soil, especially where plants have rotted off.
Apple leaf miner Astrantia leaf minerBeet leaf mining fly Celery leaf mining fly Echinops leaf miner GarlicHellebore leaf miner Holly leaf miner Holm oak leaf-mining moths Horse chestnut leaf-mining moth Insect-proof meshLaburnum leaf mining moth Leek mothLeek rustLeeksLilac leaf mining moth OnionOnion white rotPyracantha leaf-mining moth Sempervivum leaf miner
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