How to fight against the box tree borer ?

The caterpillars of this moth exclusively attack boxwood, on which they cause serious damage. If you don’t fight against the box tree moth, you risk seeing all your box trees losing all of their leaves in a short time. Let’s see what are the best solutions to get rid of this moth which, in Europe, has few natural predators.

What is the box tree moth?

The box tree moth (Cydalima perspectalis) belongs to the family of Crambidae and to the order of butterflies. It is a kind of moth from the Far East. It has been infecting boxwoods in European countries for less than 20 years (in France since 2008), because it was introduced on the Old Continent quite accidentally in the mid-2000s. Today, the box tree moth colonizes all our departments and her proliferates very quickly.

on non-stinging chenille has the following physical characteristics:

  • light green body,
  • Dark green longitudinal stripes,
  • white hairs,
  • black warts,
  • Ten abdominal sucker legs commonly called the “false legs”,
  • Head black and shiny.

This caterpillar is perfectly recognizable. To his stade imaginal (we also talk aboutimago), the box tree moth is a moth whose wingspan is between 3.5 and 4.4 cm that can easily be distinguished from other moths by the appearance of its wings edged with a brown border. They are iridescent, either of a purplish hue or of a golden hue and are mainly pearly white.

How to spot the presence of the box tree moth?

Just turn on the outside light to see a swarm of box tree moths appear. But you don’t need to be a gardening professional to suspect its presence. We see small green caterpillars, webs in the foliage of the box trees, then a yellowing of the leaves and many of them are also nibbled.

The moth attacks all species of boxwood. In a few days, the shrub can be completely stripped of its foliage… It is therefore necessary to fight against this undesirable at all costs.

The different solutions to fight against the box tree moth

To protect a boxwood against total defoliation which inexorably leads to its mortand for which the boxwood moth is solely responsible, there are several ways to get rid of this undesirable.

chemical control

This consists of using a pyrethroid-based insecticide. It is a product to be used with parsimony because, being non-selective, it is also active against the bees that we absolutely must protect.

The mechanical fight

At least the mechanical fight does not pollute the environment and one only attacks the target in this way.

You can choose toto tear out then burn all specimens with dead leaves. Note that simple uprooting followed by composting is totally inadvisable because it does not eradicate caterpillars or chrysalises. You have to use fire to destroy them.

If the boxwoods still have leaves, then everything must be done to preserve them. In this case, it is recommended to manually pick all caterpillars that we spot on the box trees and then kill them. The work is long and tedious, and does not guarantee total success because you can leave caterpillars as well as all the eggs which are deposited in the box trees by the thousands, and more precisely on the underside of the leaves.

Microbiological control

We have already seen that by using a kind of bacteria with insecticidal properties – to know Bacillus thuringiensis – we obtain good results on the box tree moth. It is an effective solution and has been used for several years for example in the gardens of Eyrignac ” Vegetable jewel of the Périgord noir », a site where this boxwood pest is rife. But in no case should the guard be relaxed. In addition, the use of this type of fight requires knowledge because Bacillus thuringiensis produces a toxin that can also kill insects that you don’t necessarily want to control.

The biological struggle

This category includes the strategy based on sexual confusion through the use of pheromones. This is also a solution that seems to work well, and that is used for example at the Domaine de Lanniron (Quimper, Finistère) whose park is under attack from the box tree moth.

Finally, you can also buy tiny waspsthem Trichogrammes, which parasitize box tree moth eggs. And why not simply attract the birds that feed on these caterpillars to your garden? This is the case with different species of tits and sparrows. We can therefore install nesting boxes, give them fat balls and seeds in winter, but also plant some shrubs giving berries which these birds are fond of. The bat is also one of the predators of this moth.

Fight against box tree moth without harming the environment is the whole problem. Some choose to cut down all their boxwood, but it is always heartbreaking to have to part with plants that have sometimes been pampered from generation to generation, the boxwood can live for several hundred years, such as this variety with a low habit so dear to our French gardens.

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