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Leaf Miner: how to recognise and treat it

Pest

Leaf Miner — Photo: Flowersabc, CC BY-SA 2.0, Wikimedia Commons

Symptoms

Winding white or brown tunnels (mines) inside the leaf, or on beet, chard, spinach and celery large pale blotches that soon turn brown and papery.
Small pale dots on the upper leaf surface where adult female flies have punctured the leaf to feed.
Heavily mined leaves dry up or drop early; badly affected tomato plants can lose most of their leaves.

Organic treatment

Pinch off mined leaves or squeeze the mines to crush the maggots; also look for small groups of white eggs on the leaf undersides.
Spare parasitic wasps and birds such as blue tits, which often keep leaf miners in check.
In a greenhouse, the nematode Steinernema feltiae can be applied against chrysanthemum leaf miner, following the supplier's instructions.

Chemical treatment

If mining is intolerable, spray spinosad on the foliage (some formulations are allowed in organic growing); follow the label dose and pre-harvest interval. Avoid pyrethroids — leaf miners are resistant and the sprays kill their parasites.

Reference information, not a guarantee. Read and follow the label of any product: dose, safety and the days to wait before harvest.

Prevention

Grow susceptible crops under insect-proof mesh, together with crop rotation so flies emerging from pupae in the soil are not trapped under the mesh.
Check transplants for mines before planting and discard infested ones.
Inspect plants regularly in summer; late-season attacks rarely do serious harm, and deeply burying mined leaves at the end of the season destroys some overwintering pupae.

Plants it affects

Sources

Figures checked against these sources.