Allium leaf miner
Phytomyza gymnostoma (syn. Napomyza gymnostoma)
Role in the garden
A small fly whose larva tunnels through the leaves and shaft of leek and other alliums. Spotted in France in 2003, in Alsace, it has become one of the main pests of garden alliums.
Activity period
Two flights: March-April and September-October
How to attract / manage it
Fine-mesh insect net during the flights, staggered planting, destruction of affected plants.
Practical guide
Where to find them
Cultivated alliums: above all leek and chives, more rarely onion, garlic and shallot. The adults puncture the leaves to feed (lines of white dots), the larvae mine the inside then pupate in the shaft as brown pupae.
Prevention
Cover allium beds with an insect net (mesh of 0.8 mm or less) during the two flight periods, plant summer leeks after the spring flight, leave no leek waste in the garden, practise a long rotation.
Early signs
Rows of small white dots on the leaves (feeding punctures of the adults), twisting leaves, then brown tunnels in the shaft and brown pupae visible between the sheaths.
Action / control
No effective curative treatment in the garden: pull up and dispose of (without composting) the mined plants to destroy the pupae, and rely on the net for the next crop.
Sources
- INRAE, Ephytia : VigiJardin, Mouche mineuse du poireau (Phytomyza gymnostoma)
- FREDON Nouvelle-Aquitaine : fiche synthèse Mouches du poireau (2023)
- Jardiner Autrement (SNHF) : fiche Poireau, mouche mineuse
Favourite plants / resources
Related plant entries
Leek
A traditional ally of the carrot: its sulphur compounds are reputed to confuse the carrot fly (Psila rosae), on the model of the onion, whose effect has been measured (Uvah and Coaker, 1984). Earth up during growing to blanch the stem.
Onion
The sulphur compounds released by the bulbs are reported to repel several pests (the carrot fly in particular), an effect documented in the laboratory, moderate in the garden. Like the other alliums, tradition keeps it away from legumes, with no effect on their nodulation demonstrated in the field.
Garlic
Reputed to repel aphids and certain insects via allicin and sulphur compounds (in vitro effect). Widely used in the apple-tree guild in permaculture tradition.
Chives
A clump-forming perennial, traditionally planted at the foot of fruit trees and strawberries (its sulphur compounds are reputed to hinder some insects and fungi). Mauve pompom flowers, richly nectar-bearing and much visited by bumblebees and hoverflies, precious helpers. Divide every 3-4 years to renew it.