Crop damage caused by the allium leaf miner

First detected in the UK in 2002, the allium leaf miner has since spread, particularly in the Midlands. Initially a pest of allotments and gardens, it now damages commercial crops of onion, leek, and garlic.

Scientific name: Phytomyza gymnostoma

In the UK, it probably has two generations per year: the first generation lays eggs in March/April, while the second generation lays eggs in October/ November.

Before laying eggs on the stems or bases of leaves, the female flies puncture leaves and suck up the exuding sap. This causes distinctive lines of white dots on the foliage. The larvae make tunnels in the foliage, stems and bulbs. Pupation takes place mainly within the stems and bulbs, but some pupae may end up in the soil, especially where plants have rotted off.

Plants affected by allium leaf miner tend to rot because of secondary infections from fungi and bacteria that develop in the damaged tissues.

Protect plants with insect-proof netting at times when the adult flies are active and laying eggs.