How to fight against the boxwood moth?

The caterpillars of this lepidopteran attack exclusively the boxwood on which they cause serious damage. If we do not fight against the boxwood moth, we risk seeing all of its boxwoods lose 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 boxwood moth?

The boxwood moth (Cydalima perspectalis) belongs to the family of Crambidae and to the order of butterflies. It is a kind of lepidoptera 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 boxwood moth colonizes all our departments and her proliferates very quickly.

Her non-stinging caterpillar has the following physical characteristics:

  • Light green body,
  • Longitudinal streaks dark green,
  • White hairs,
  • Black warts,
  • Ten abdominal suction cups that are commonly called “prolegs”,
  • Black and shiny head.

This caterpillar is perfectly recognizable. To his imaginal stage (we also speak ofimago), the boxwood moth is a nocturnal butterfly 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 a purplish hue or a golden hue and are predominantly pearly white.

How to spot the presence of the boxwood moth?

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

The borer attacks all species of boxwood. In a few days, the shrub can be completely stripped of its foliage… We must therefore fight against this undesirable at all costs.

The different solutions to fight against the boxwood moth

To protect a boxwood against total defoliation which inexorably leads to its dead, and 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 insecticide. It is a product to be used sparingly because, being non-selective, it is also active against bees, which we must imperatively protect.

Mechanical struggle

At least the mechanical control does not pollute the environment and that way we only attack the target.

We can choose tosnatch then burn all specimens with dead leaves. Note that simple uprooting followed by composting is not recommended because it does not eradicate caterpillars or pupae. We must resort to fire to destroy them.

If the boxwood still has leaves, then everything should be done to preserve them. In this case, it is recommended to manually remove all tracks that we see on the boxwood and then kill them. The work is long and tedious, and does not guarantee total success because we can leave caterpillars as well as all the eggs which are deposited in the boxwood 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 – good results are obtained on the boxwood moth. It is an effective solution and has been used for several years for example in the gardens of Eyrignac ” Plant jewel of the Périgord noir », A site where this boxwood pest is rampant. But under no circumstances should the guard be released. In addition, the use of this type of fight requires knowledge because Bacillus thuringiensis produces a toxin that can also destroy insects that you do not necessarily want to control.

The biological struggle

This category includes the strategy based on mating confusion through the use of pheromones. It 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 boxwood moth.

Finally, we can also buy tiny wasps, the Trichogramma, which parasitize the eggs of boxwood moths. And why not simply attract the birds that feed on these caterpillars to your garden? This is the case for the 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 lepidoptera.

Fight against the boxwood 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 we have sometimes pampered from generation to generation, the Boxwood can live for several hundred years as for example this variety with low bearing so dear to our French gardens.