Latin name: Delia antiqua
Plants affected: Onion, shallots and leeks
Main symptoms: Yellowing and wilting of leaves, damaged bulbs and seedlings killed
Caused by: Larvae of a fly
Timing: June and July
What is onion fly?
Seedlings affected by onion fly can be killed. On older plants outer leaves can yellow and wilt. The onion bulb can be destroyed as the larvae feed within it. This insect is most often encountered in central and eastern England and is most damaging during June and July.
Bean seed fly can also be a problem on allium crops and can reduce seedling emergence (particularly of salad onion) dramatically.
- There are no insecticides available to home gardeners for controlling onion fly
- Badly damaged plants found towards the end of summer should be lifted carefully and burnt to prevent maggots from completing their development.
- Some protection may be gained by using insect-proof mesh
- A mixture of pathogenic nematodes, sold as 'Fruit and Vegetable Protection', can be watered into the soil which may control the young larvae, this is available by mail order from biological control (pdf document) suppliers
- Growing onions and shallots from sets, rather than seeds, can help plants to survive attacks by the first generation of larvae
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