The boxwood moth is a small butterfly that was introduced to Central Europe from East Asia at the beginning of the 21st century. The first specimens were reported in Germany in 2006. As beautiful as the butterflies are to look at with their silky white wings and brown border, they do a lot of damage to the popular box trees. On average, the boxwood moth is about 5 centimeters long as a caterpillar shortly before pupation. As a fully grown butterfly, its wingspan reaches up to 4.5 centimeters. Since they only appeared so recently in Germany and the surrounding countries, the level of knowledge about their behavior and the most effective method of combating them are still very limited. The first notable progress was made in 2012. We report on this below.
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Control of the box tree moth
It seems like a diversionary maneuver, because the moths themselves do not sit on the box trees, but on other plants. However, during their short lifespan of around 8 days they lay their eggs in the box. The young caterpillars are initially about 5 millimeters long, with light-dark stripes on the green body. By the time they pupate, they grow to a length of 5 cm, which makes it difficult to control them.
Scientists assume that under the weather conditions in Germany 2 to 3 generations of the box tree moth grow up every year, which explains the explosive multiplication. The caterpillars of the last oviposition form protective cocoons inside the book for wintering, so it is crucial that their control is started before winter. If you also carefully search your box trees for these gray-colored cocoons during the winter and cut out the infested areas immediately, you can, with a bit of luck, fight the danger before the next devastation.
From March, when the outside temperature is around 7 ° -12 ° Celsius, the devouring continues, while the caterpillars pass through six to seven larval stations. In doing so, they prefer to destroy the common boxwood, as can be found in many private gardens and plants. The caterpillars first eat the leaves and then attack the green twig bark, which also causes large box trees to die. Only the leaf bark and dried up leaf tissue remain. Since the caterpillars are able to spin threads, the infested box trees are mostly surrounded by a thick web. One glimmer of hope in this disaster is the possibility that infected box trees will sprout again after a while. The lifespan as a butterfly is then limited to a few days, which is sufficient, however,
Early detection of infestation
The earlier a boxwood moth infestation is recognized on a box tree, the greater the chances of success in combating it. The hobby gardener should therefore examine his boxwood stock for bright spots every day between March and October, because these are the first noticeable signs of the presence of the caterpillars. It is important to look for the pests deep inside the plants, because this is where they often stay. At this early stage of the infestation, picking up the caterpillars immediately may be enough to get rid of these wolverines. As a supportive measure, it is advisable to additionally prune the boxwood vigorously and to dispose of the clippings with the residual waste.
Since the caterpillars are also able to form threads, they use this ability to form small protective chambers by gluing the leaves together. In this way, they are also able to rappel down on the run with lightning speed, similar to how the spiders. So if gray webs appear on the plant, the experts assume that collecting in connection with pruning is no longer sufficient to save the boxwood. In this case, the hobby gardener is forced to resort to the more effective methods of pest control.
Chemicals
If the caterpillars have already penetrated deep into the boxwood, it may be inevitable to resort to chemical sprays to save the laboriously grown plant. So far, the use of the insecticide thiacloprid has been very successful. In Germany and Switzerland, this spray is also approved for use in private gardens to combat numerous biting and sucking insects, including the box tree moth. However, the product is labeled by the EU as harmful and should be used taking all precautionary measures, especially since it has to be applied with high pressure in order to penetrate deep into the interior of the boxwood.
- Bayer Garden Pest Free Calypso,
- Celaflor Pest Free Careo
- Celaflor Naturen Pest-free Neem
The following protective measures should be carefully observed when these chemical agents are used to control the box tree moth:
- The minimum distance from the user is 1 m;
- The minimum distance between bystanders is 3 m;
- Protective suit must be worn by the user;
- Gloves;
- Head, eye and respiratory protection;
- possibly an additional rubber apron;
- Rubber boots.
The hobby gardener should take these protective measures seriously when using pesticides, because the damage to health should not be underestimated.
Biological methods of control
Since the plague of the box tree moth has only spread in the local regions for a few years, it was only possible to collect well-founded knowledge of the application of biological procedures to a lesser extent. However, considerable successes in control have already been achieved with the following methods:
Pressure Washer and Foil
This technique is as simple as it is effective. The infested box tree is sprayed vigorously with a high-pressure cleaner, deep into the interior of the plant. The caterpillars fall onto the film spread out underneath and can be disposed of in the residual waste.
Pheromone traps
This technique is also called attractant trap because the messenger substances of the insects are used here to attract the male moths of the box tree moth. Instead of the hoped-for female, however, a cardboard box covered with glue awaits them, from which they can no longer escape. In this way, the population cannot be eliminated completely. In any case, the number of matings and the associated offspring can be significantly reduced.
Confusion method
This tactic of combating also uses pheromones, but on a different principle than in the case of the attractant trap. Artificially produced pheromones are sprayed on the boxwood plants, which confuse the male butterflies so much that they can no longer locate the females. This also demonstrably reduces the number of pairings.
Light traps
Since the moths also fly in the dark, attempts have been made to fight them with light traps. These attract the moths with a high proportion of blue light or ultraviolet radiation. The most effective spectral ranges are in wavelengths that are invisible to humans. The catch radius is, however, quite limited at 10 to 15 meters. With regard to the effectiveness of light traps, it remains to be seen what experience will be gained in the coming years.
Neem oil
Since the boxwood moth come from the East Asian region, the farmers there have been able to gain a lot more experience with regard to control in order to render these pests harmless. They achieve good results in the use of neem oil, which is obtained from the seeds of the neem tree. Caterpillars that come into contact with this agent die immediately afterwards.
Delfin, the biological agent from Switzerland
Since the first box tree moths caused enormous damage to the box tree population in Switzerland, the breeders and researchers there have the most sophisticated control strategies at their disposal. Good experiences have been achieved with the biological agent dolphin. As a natural insecticide, it works specifically against the caterpillars. At the same time, it is harmless to people, pets and the environment. Therefore, nothing speaks against the use of dolphins in the private garden, on the balcony and terrace in order to successfully control the box tree moth. As soon as the outside temperature is at least 12 ° Celsius, the poison can be used. The smaller the larvae, the greater the chances of success. Dolphin is a powder that is dissolved in water and sprayed onto the infested box trees with a suitable sprayer using a lot of pressure.
Emergency treatment for larger caterpillars
In the event that the box tree moth infestation is discovered too late, the agent Pyrethrum FS has proven its worth. From a size of 3 cm, the biological agent dolphin is no longer sufficient to get rid of the caterpillars. If you still shy away from the highly toxic insecticides in this case, Pyrthrum FS is an alternative to successfully combat the pests. Although this remedy consists of a natural plant extract, it is nevertheless not gentle on beneficial organisms. At this point, attention should be drawn once again to the need to treat the box trees deep inside. This inevitably means that the user comes very close to the plant and the areas that have already been treated. It is therefore essential to ensure that you have adequate protective clothing.
No natural predators
According to the knowledge of gardeners, breeders and researchers so far, the caterpillars of the box tree moth have no natural predators. Birds spurn them entirely or spit them out again. The reason for this is obviously that the caterpillars ingest the poison from the boxwood, making them incompatible with other animals. It has been observed occasionally that wasps tear apart the caterpillars. However, this is not enough to effectively combat the plague. Only the moths are eaten by birds.
Neither chemical nor biological agents work during hibernation
Depending on the length of the day, the caterpillars of the last oviposition begin to hibernate towards the end of September. For this purpose they form cocoons in a protective web of threads and leaves. They stay there until next spring and become active again from March or April as soon as the outside temperature reaches around 12 ° Celsius. So far, no agent has been developed that would be able to penetrate the cocoons and webs during hibernation. Anyone who nevertheless discovers such spots in the box tree during the winter can simply cut them out.
The greater diversity of boxwood species deprives the boxwood moth of its livelihood
Since the pest only attacks the common boxwood (buxus sempervirens), the experts advise increasing the biodiversity in the cultivation of this popular plant. There is nothing to prevent the Asian buxus microphylla, the Chinese buxus bodinieri or the Spanish buxus balearica from being established in the Central European regions. In view of the spreading plague, efforts of federal tree-viewing are being intensified in order to discover the best alternatives among the more than 100 different types of box tree that are not attacked by the box tree moth.
First successes
The box tree moths have been attacking the lovingly grown box trees in Germany since 2006. They were probably brought in with deliveries of goods from the East Asian region and have since spread from year to year. The damage that the voracious caterpillars have caused so far runs into the millions. In Switzerland in particular, huge, ancient box hedges fell victim to them. As knowledge was gained about the way of life and reproduction of the box tree moth, effective means of control could be developed. There are now a number of biological, chemical and mechanical methods to choose from, which are quite promising.
