Allium Leaf Miner
In the garden: Ornamental alliums
On Crops: Onion, leek, chives, garlic, and shallots
Since first appearing in the UK in 2003, this fly can now be found throughout southern and eastern England and is also spreading to other areas . Also prevalent in Eastern Europe.
The adult allium leaf miner is a small dark-coloured fly approximately 3mm in length. The female flies make small puncture marks into the tips of leaves and lay eggs into the plant tissue. Eggs hatch into maggots that burrow down into the plant creating tunnels as they feed and grow. The maggots turn into small brown pupae at the base of the plants, either remaining in the mine or breaking out between the stem and the leaves.
Puncture marks where the female flies have been laying eggs appear as a series of white dots on the tips of leaves. The resulting maggots produce mines that run down through the plant, often resulting in rotting that can eventually destroy the whole plant.
Eggs are usually laid at the end of April and again during October and November. Covering plants with a fleece during these periods will help to reduce the number of egg-laying flies from accessing the plants.
Once the maggots have started to mine into the plants there is little that can be done to control them. Where plants are clearly infested they should be removed from the crop to prevent the next generation of flies from emerging.
Infected crops should be removed during the winter months when the pupae are dormant. Those that may be within the soil can be exposed to insectivorous birds by regularly digging the soil.