The allium leaf miner, which originates from Eastern Europe, appeared in France in the early 2000s. At present, it is mainly common in the northern part of France, but it is gaining more and more ground. This dipteran, also known as Napomyza gymnostoma, is harmful to leeks as its name indicates, but also to plants of the same genus Allium such as chives, garlic and onions.
Characteristics of the leek fly
Allium leaf miner also have moths or leek worms as enemies, but it should not be confused with them. The allium leaf miner is a small insect measuring about 3 mm in length. The yellowish larvae will start to make galleries in the leek leaves, from the green to the white part. This action greatly weakens the plant and makes it sensitive to bad weather. As they develop, these larvae will become small cocoons with the appearance of a grain of rice, the pupae.
Attacks occur in two stages, in spring and autumn. After winter, the cocoons already present on leeks in the garden will transform into flies, feed by stinging the leeks and will also mate and infest the available leeks. This results in deformities in the leaves of the affected leek, on which characteristic white spots can be seen, caused by the fly feeding on the plant's sap. Leeks infected in this way cannot be eaten. In autumn, the flies emanating from the spring larvae will emerge and will thus be able to continue their reproduction cycle.
Controlling the allium leaf miner
To protect your garden from allium leaf miner attacks, it may be wise not to sow or plant leeks in the same place from one year to the next. In other words, crop rotation is highly recommended to avoid contamination by larvae that may be in the soil. A physical barrier can also be used by using a sufficiently thincrop veil that will prevent flies from infecting the leeks, either to feed or to lay eggs. This veil should be put in place in early spring, before the flies start to appear in the garden.
If larvae are found in leek leaves, they should not be put in the compost at all costs. The larvae can survive and continue to contaminate the vegetable garden. Some wasps may be able to help eliminate allium leaf miner and may be attracted to plants such as yarrow, tansy or St. John's wort. Tansy, lovage or wormwood-based purines are also said to be natural leek fly repellents, although there is no scientifically proven evidence of this.