Miner flies: recognize and combat damage

Ornamental plants in particular are affected by the annoying pests. We show how to recognize the leaf miner, prevent it and fight it properly.

The damage caused by the leaf miners can be seen on the leaves of a wide variety of plants and also poses a visual problem for many gardeners. Here's everything you need to know about the leaf miners that cause this damage and what you can do about them.

miner flies (Agromyzidae) belong to the suborder of flies (Brachycera) and represent very small flies. The larvae of the leaf miners have a special way of eating through the infested leaves, because they mine through the leaves. Hence the name of the miner flies. What is meant by mining is explained below.

Miner flies: fact sheet

The miner flies are very small, dark-colored flies with a body size of two to three millimeters. The females have a saw-shaped ovipositor for laying eggs, which is also called the ovipositor. The females use this ovipositor to lay their eggs in the plant tissue – from which the whitish-yellow larvae then hatch. The larvae are so-called leaf miners, which feed on the leaves without injuring the outermost skin of the leaf - they eat mines into the leaf tissue, so to speak. Depending on the type, these feeding patterns differ and spiral, gang, space or bubble mines can occur.

When the development of the larvae is complete after three larval stages in the leaves, they eat an exit hole in the leaf and thereby leave it. They then pupate in the soil or on the plants and complete their development. The development of a new generation takes about 25 days at a temperature of 20 °C.

The adult leaf miners pierce leaves and suck out the plant sap for their sustenance. These puncture sites and the puncture sites of the ovipositor are then entry points for bacteria and fungi, such as fusarium, and can thus cause further damage to the plants.

Common miner fly species

In Germany alone there are already 550 different leaf miner species, worldwide there are around 3,000 species. Below we present some of the best-known and most frequently occurring miner flies.

tomato leaf miner (Liriomyza bryoniae)

The tomato leaf miner not only damages tomatoes (Solanum lycopersicum), but also many other crops, however, this leaf miner causes most damage to tomatoes, salads (Lactuca sativa) and cucumbers (Cucumis sativus). This leaf miner can be found in North Africa, North Asia and Europe. The adult leaf miners are black and yellow in color, the larvae are whitish to transparent and as the larvae get older they develop a yellow head. This miner fly can be found both outdoors and in greenhouses.

Florida leafminer (liriomyza trifolii)

As its name suggests, this leaf miner is not native to Europe, but was introduced from North America in the 1970s. The Florida leaf miner infests a wide variety of ornamental and vegetable plants. The adult leaf miners are yellow-black in color and the larvae are ocher in color.

South American leafminer (Liriomyza huidobrensis)

The South American leaf miner is also an introduced pest that originally comes from South and Central America. This leaf miner fly is also called leaf vein miner fly and was introduced to Europe in 1987 - it damages almost all vegetable crops. Plant material has spread this leaf miner worldwide and is particularly harmful to leafy greens. The larvae of the South American leaf miner are off-white and transparent.

Pea Leaf Miner (Phytomyza atricornis)

The adult pea miner flies are black in color and prefer to lay their eggs in peas (Pisum sativum) and kidney beans (Phaseolus vulgaris) away. The larvae eat conspicuous leaf mines into the leaves, however the damage done by the pea miner fly is of minor importance. It is therefore usually not necessary to combat the pea miner fly.

leek leafminer (Phytomyza gymnostoma)

This miner fly makes itself particularly about onions (Allium cepa) and leek (Allium porrum) here. Winter leeks are particularly popular with leaf miners, and the larvae feed downward towards the base of the leek. The mines can also rupture and the base of the leek can be injured by the larval feeding. This can also lead to rot.

onion leaf miner (Liriomyza nietzkei)

Onions are more damaged by onion leaf miners than leeks. Here, too, the larvae eat mines into the plant tissue. As a result of this feeding activity, the foliage bends and begins to wither. The females of the onion leaf miner cause punctiform injuries on the young onion plants.

Recognizing leaf miners: symptoms and damage

Leaf miners often infest ornamental crops such as chrysanthemums (chrysanthemum) or gerberas (gerberas). The leaf miners cause direct damage through the piercing of the leaves by the females and through the mines that the larvae eat into the leaf tissue. These burrows and leaves dry out, the leaves often fall off prematurely. Of course, the loss of leaves also reduces the yield of vegetable crops, since the assimilation area is smaller.

Secondary damage occurs when fungi and bacteria penetrate the leaves and thus the plant through these injuries. In addition, some leaf miners can also carry viruses such as the tobacco mosaic virus or the English curling disease transmitted to the May beet and thus damage the plants.

Prevent miner flies

Crop protection nets can be used to prevent an infestation with miner flies, as these prevent the small pests from laying their eggs on the leaves. This requires close-meshed culture protection nets through which the small adult flies cannot get through to lay their eggs.

With the use of yellow boards, an infestation can be recognized early on. Here you can find out more about Use of yellow boards and how to use them properly.

Fight miner flies

If you have an infestation with leaf miners, it's time to think about controlling the small flies and their voracious caterpillars. Below you will find out what options are available to you to combat leaf miners.

Chemically combat miner flies

The chemical control of leaf miners can be done with insecticides containing the active ingredient spinosad. This active ingredient is approved as a plant protection agent in organic farming, but unfortunately it is dangerous for bees and must therefore not be applied to flowering crops.

You can either inject or spray insecticides with Spinosad. This remedy is not only suitable for combating leaf miners, but can also be used against thrips (Thysanoptera), Colorado potato beetle (Leptinotarsa ​​decemlineata) or the cherry vinegar fly (Drosophila suzukii) use.

Combat leaf miners biologically

An effective biological control method for leaf miners is the use of beneficial insects such as parasitic wasps (Dacnusa sibirica or Diglyphus isaea). The parasitic wasp Dacnusa sibirica parasitizes the first larval stages of the leaf miner by laying an egg in the larvae with its ovipositor. The larvae of the parasitic wasps then hatch from this egg and feed on the leaf miner, which then dies. The parasitic wasp Diglyphus isea on the other hand, the leaf miner larva paralyzes and then lays an egg next to the leaf miner. After the wasp hatches, this larva feeds on the stunned leaf miner larva. After pupation, useful parasitic wasps hatch again and go in search of new leaf miners.

At low infestations or early infestations with leaf miners is the simplest method of control removing the affected leaves, because they also contain the harmful larvae of leaf miners. However, do not put these leaves in the compost, but place the infested plucked leaves in a plastic bag and dispose of it with household waste.

Tip: Our Plantura pest-free neem can also be used against leaf miners. It is obtained from a herbal and natural active ingredient from the seeds of the neem tree and is not harmful to bees.

Fight leaf miners with home remedies

An effective means of deterring the leaf miners is the use of nettle manure, because its smell deters the leaf miners. In addition, the liquid manure also strengthens your plants. For nettle manure you only need water and nettles (Urtica), which you have to ferment in order to obtain an effective plant protection and plant strengthener. Here's how to get one nettle manure made and used correctly.

Summary combating leaf miners:

• Chemical control uses the active ingredient spinosad, which, however, poses a risk to bees, which is why we recommend alternative control
• Biological control is most effective with beneficial insects such as parasitic wasps; if the infestation is less severe, the affected leaves can simply be removed, which are then disposed of with household waste
• Nettle manure is excellent as a home remedy, as it also strengthens the affected plant

More home remedies control of pests in your garden can also be found here in our special article.