If the leaves or needles of thuja and other woody plants suddenly turn brown, the leaf miner may be behind it. In this article, you will learn how to get rid of the stubborn pest.

The leaf miner leaves true works of art on the affected leaves

Table of Contents

Show all
  1. the essentials in brief
  2. What are leaf miners?
  3. damage picture
  4. Combat leaf miners
  5. frequently asked Questions

    6. the essentials in brief

    • The leaf miner is a tiny, inconspicuous butterfly.
    • It mainly lives in deciduous trees and its caterpillars eat through the leaves.
    • These turn brown and eventually fall off.
    • Leaf miners are combated with scissors and sprays as well as with preventive measures.

    What are leaf miners?

    Leaf miners are very small, fairly inconspicuous butterflies that have only appeared in Europe since the 1970s. In particular, the Thuja leaf miner - one of the approximately 230 European species - has been feared by hedge owners since the 1990s because of its invasive appearance. The different species are mostly specialized on certain host plants, after which they are named. The moths live in trees and other shrubs, and their caterpillars in particular cause a great deal of damage. The little animals live as so-called miners, i. H. they mainly eat through the leaves of the plants and thus damage them.

    This is what the pest looks like

    The external appearance of leaf miners and their caterpillars differs depending on the species. However, all varieties have certain characteristics in common:

    • very small moths with a small wingspan between five and nine millimeters
    • only rarely slightly larger
    • mostly flesh to olive colored body
    • other colors are also possible
    • fringed wings
    • pronounced proboscis
    • Caterpillars remarkably flat and, depending on age, up to about 5 millimeters long
    • The appearance of the caterpillars depends heavily on the respective larval stage

    Knowledge of the way of life important for efficient control

    Most leaf miner species are active very early in the year and start flying around April. The pests hibernate as caterpillars or even adult moths in fallen leaves or leaves remaining on the tree, but they can also hide in the tree bark. The females lay up to 40 eggs, from which the larvae hatch within only two to three weeks. These immediately begin their work of destruction and bore into the inside of the leaves in order to eat passages in the tissue. After a total of five larval stages, the caterpillars pupate in these tunnels, which can usually be seen with the naked eye.

    The pupae of the leaf miners are clearly visible

    Depending on the type and weather, up to four generations of leaf miners develop each year, which are not limited to just one tree. On the contrary: if it is warm and dry, all neighboring trees and shrubs are also affected in no time at all due to the rapid development. For this reason, it is important to act as early as possible in the event of a suspected infestation. This is the only way to prevent the plague from spreading. If leaf miners have ever appeared in your area or in your neighborhood, you should take appropriate precautionary measures. This includes, above all, always clearing away and disposing of autumn leaves.

    digression

    This butterfly damages chestnut

    If chestnuts get brown leaves early in the year, the horse chestnut leaf miner (Cameraria ohridella) is often behind it. This pest has also only appeared in Central Europe for a few decades, but has quickly become a problem for white-flowered horse chestnut trees. As a rule, only this variety of the deciduous tree is attacked, red-flowering varieties are not of interest to the butterfly. The horse chestnut leaf miner moth is not closely related to the members of its family that are native to us and, with its orange-brown coloration, also shows a completely different appearance. However, the same rules apply to them when it comes to control methods.

    Malicious image - How to recognize a miner moth infestation

    Typically, infested plants quickly turn brown from a leaf miner infestation. You can find out what other causes lead to thuja turning brown in the following video.

    youtube

    The damage caused by the feeding activities of the caterpillars can be seen very quickly due to the often massive occurrence. However, most of the damage is only visual: the infested tree looks ugly, but is not directly endangered. Trees damaged by leaf miners rarely die, as the butterflies prefer to populate larger and therefore more resistant specimens. Typically, the damage is manifested by:

    • an unsightly browning of the leaves or needles even in early summer
    • mostly deciduous trees are affected, but some conifers (Thuja) are also endangered
    • this is followed by early leaf fall
    • heavily infested trees often limit their growth
    • Reduction in flowering (especially in lilacs) or formation of fruit (chestnut)

    In some cases, trees infested with leaf miners often start flowering again in late summer or even autumn - when the tree has recovered from the infestation. Deciduous trees develop new, healthy leaves the following spring. Only conifers like the Thuja look permanently unattractive, since the brown needles do not turn green again even after the pest has been successfully combated.

    These plants are particularly frequently attacked by leaf miners

    Maple leaves taste particularly good to leaf miners

    The thujas (trees of life), which are so popular for dense hedges, and horse chestnuts are particularly frequently attacked by the voracious leaf miners. These tree species are also endangered:

    • Maple (Acer)
    • Black locust or false acacia (Robinia pseudoacacia)
    • Azaleas (Rhododendron molle and other species)
    • Lilac (Syringa)

    It is also evident that the pests are also increasingly conquering other host plants. Apparently, the moths are not fully specialized, but can increase their range of prey. Therefore, pay attention to a possible infestation, especially with stone and pome fruit trees and generally with deciduous trees. This is especially true if other trees - such as the Thuja hedge - are already infested in your garden.

    Combat leaf miners

    Affected leaves should be discarded

    Unfortunately, leaf miners are difficult to combat once you have the infestation on the tree. Therefore, preventive measures are all the more important, especially collecting the fallen leaves - in this way you prevent a new plague in the following year.

    pheromone traps

    Pheromones are certain sex attractants that female leaf miners use to attract males to mate. Special pheromone traps are commercially available, which you hang in the trees and which then capture the male moths. The animals get stuck on the glue fixed in the trap and can no longer escape. Although attractant traps reduce the infestation pressure, since fewer male moths also mean fewer fertilized females and thus fewer caterpillars, they are not suitable for combating them alone. With their help, however, you can determine whether there is a leaf miner infestation at all and how severe it is. Then you'd better take effective countermeasures.

    tips

    Hang the pheromone traps in endangered trees as early as April and leave them there until the middle or even the end of October.

    Spraying with nettle manure

    "Why do you need chemical sprays if you can cheaply produce completely non-toxic plant manure yourself?"

    Spraying with nettle manure has also been shown to be effective against the leaf miner, but not in the case of an acute infestation. Regularly spray endangered trees as a preventive measure, starting as early as April at the latest and continuing until late autumn. The method is therefore quite complex and sometimes difficult to carry out with large trees - such a horse chestnut can at least grow up to 30 meters high. However, spraying is practical for smaller trees, such as thuja, lilac or rhododendrons.

    Nettle manure is a cheap, environmentally friendly way to combat the leaf miner

    How to prepare the nettle liquid manure:

    1. Gather a kilogram of nettles.
    2. These should not bloom if possible.
    3. Otherwise you can use the whole plant including leaves and stems.
    4. Chop the herb, as the active ingredients then dissolve better.
    5. Place the plant material in a plastic bucket.
    6. Do not use a metal container, this will lead to undesirable chemical reactions.
    7. Pour ten liters of rainwater on it.
    8. Add a handful of rock flour ($15.00) (against the unpleasant odor that develops later).
    9. Place the bucket in partial shade.
    10. Cover it with a mosquito net, beach mat, etc.
    11. After about eight to ten days, the liquid manure is ready and can be used.

    Spray the shrubs every two weeks between March/April and September/October. Filled in canisters, the finished liquid manure lasts for about a year.

    Injection with neem

    Spraying with the natural insecticide neem (or neem), an agent obtained from the Indian neem tree (Azadirachta indica), also has an anti-feeding effect on the caterpillars of the leaf miner and damages them in their development. However, neem products are quite expensive, which is why the regular treatment of a large tree is no longer in a reasonable cost-benefit ratio - especially since neem also has an impact on other insects. Similar to the self-made nettle manure, it is used here primarily for smaller trees.

    digression

    Are there any pesticides against leaf miners that are approved for home and hobby gardens?

    For the hobby gardener, the selection of effective plant protection products is very small, since their use in the house or small garden is either forbidden or only possible with appropriate proof of expertise. This also applies to the often recommended remedy Calypso from the manufacturer Bayer. The other remedies against leaf miners available on the market and approved for the hobby garden all work on the basis of natural active ingredients, such as garlic or neem.

    Regular pruning

    Regular pruning protects the Thuja from leaf miner infestation

    Regular pruning, especially of endangered Thuja hedges, together with spraying, is an effective way of preventing leaf miner infestation. You should proceed as follows:

    • Cut back thujas in early spring
    • start spraying (e.g. with nettle liquid manure) at the same time
    • Cut back again in July
    • at the same time further spraying with stinging nettle liquid manure

    Never dispose of the clippings in the compost, but with household waste or burn them.

    Collect and dispose of fall leaves

    Another very effective remedy against annoying leaf miners is this: carefully collecting and disposing of fallen leaves, especially autumn leaves. Be very consistent in this respect, so that no leaf is left lying around and the little animals wintering in it can possibly cause a new plague in the following year. Do not dispose of the leaves on the compost, as the moths will continue to develop here and will still hatch the following spring. Instead, throw the leaves in the trash or, even better, burn them. Of course, the latter is only possible if the burning of garden waste is permitted in your residential area. This method is particularly useful for infested horse chestnuts and other large deciduous trees.

    tips

    If you would like to plant a chestnut in your garden, choose the scarlet horse chestnut (Aesculus x carnea 'Briotii'), which is resistant to leaf miners. Experience has shown that this is spurned by the little animals.

    settle predators

    Birds like to eat leaf miners

    Like so many other pests, the leaf miner has natural enemies who literally love to eat the butterfly and thus decimate the population without any further action on your part. These include, in particular, some songbirds such as tits, which you can lure into your garden with a few nest boxes hung in endangered trees and strategically placed feeding stations. Please note that the feathered pesticides only feel comfortable with you if you make your garden bird-friendly:

    • No use of chemical pesticides (especially no insecticides!)
    • these destroy the birds' food base and also poison them at the same time
    • a dense stock of trees and other shrubs, preferably native species
    • dense hedges, ideal for nesting
    • Feeding places, not only in winter
    • several nest boxes

    In addition to birds, parasitic wasps (€22.99) are natural opponents of leaf miners. You can buy these - completely harmless - beneficial insects in specialist shops and settle them in endangered trees. The advantage of such a measure is that parasitic wasps are also effective against a whole range of other garden pests.

    Further measures

    Since leaf miners also often hide in the tree bark during the winter months, you should surround the trunks of endangered trees with glue rings or coat them with a mixture of wallpaper paste and lime in early autumn. In this way, the animals cannot retreat into the bark, which means that another place of retreat remains blocked.

    frequently asked Questions

    In which season are leaf miners particularly active?

    Leaf miners are mainly active two times a year, so adjust your control strategy (spraying and cutting) accordingly. The main peaks in moth activity are in early spring, mostly in April, and again in July/August. But even in the meantime, if the weather is suitable, further generations can fly out, which is why regular spraying with biological agents is so important.

    What to do if there are leaf miners in the apartment?

    In rare cases, such as when there is an infected tree near a window, leaf miners can also get into the house or apartment and wreak havoc on indoor plants. Therefore, keep doors and windows closed or provide them with an insect screen as soon as you suspect an infestation. However, the leaf miners do not eat food such as flour, etc., as this is not their natural food. If you find moths in your supplies, they are definitely flour moths (Ephestia kuehniella), which look very similar to leaf miners.

    tips

    If you have chickens, you should let them roam free in the ornamental garden or orchard. The busy animals scratch and peck at beetles and larvae lying on the ground all day long, which is why they also get rid of the leaf miner larvae (and other pests) in fallen leaves.

Category:

Animals in the garden