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Natural corn borer control - With ichneumon wasps against the European corn borer

Average reading time: 4 minutes

It is and still remains one of the most important pests in maize: the European corn borer. Due to climatic changes, it is spreading more and more also in Germany and causes holes, broken plants and perhaps even damage to the maize cobs. To minimise yield and quality losses, the pest can be controlled at different stages chemically, mechanically or biologically. For example, with ichneumon wasps (Trichogramma), the natural enemies of the European corn borer.

But before we talk about corn borer control, let's understand the pest itself.

bleibt einer der bedeutendsten Schädlinge im Mais: der Maiszünsler. Aufgrund klimatischer Veränderungen breitet er sich zunehmend auch in Deutschland aus und sorgt für Bohrlöcher, abgeknickte Pflanzen und gegebenenfalls sogar für Schäden an den Maiskolben. Um Ertrags- und Qualitätseinbußen zu minimieren, kann der Schaderreger in unterschiedlichen Stadien chemisch, mechanisch oder auch biologisch bekämpft werden. Zum Beispiel mit Schlupfwespen (Trichogramma), den natürlichen Feinden des Maiszünslers.

Doch bevor es um die Maiszünslerbekämpfung geht, wollen wir den Schädling an sich verstehen.

European corn borer (Ostrinia nubilalis)

The European corn borer is a small butterfly. However, it is not the butterfly that causes the damage to maize, but its caterpillars. They perforate the stalks and cobs. The result are weak spots. Damages caused by the caterpillars of the European corn borer are:

  • Broken maize stalks, especially in the lower area.
  • Disturbed water and nutrient supply
  • Potential infection spot for fungal diseases and bacteria

Infestation begins with the migration of the moths from the maize population of the previous year. Depending on the region, it starts in June and is most intense in July. Once in the population, the females lay their eggs preferably on the lower side of the leaves. One to two weeks later, the larvae of the corn borer hatch and begin to spread to the neighbouring plants and bore into the upper part. In the course of vegetation, the caterpillars eat their way through the inside of the stem from top to bottom.

After the harvest, they remain at the base of the stalk and can overwinter in the maize stubbles that remain in the field. The following May, pupation takes place. Thus, the cycle and also the spreading starts anew.

One of the most important ways of combating the European corn borer, thus, is the effective damage of the maize stubbles during stubble cultivation, e.g. by means of a knife roller. This prevents the larvae from overwintering.

Distribution of the corn borer

It is with good reason that it is called the European corn borer. The origin of the European corn borer is in Southern and Central Europe. Later, it was introduced into North America and, in the meantime, has spread all over the world.

The distribution is encouraged by the following points:

  • Good adaptability of the pest
  • Increase of maize cultivation areas
  • Good climatic conditions favoured by climate change

Ichneumon wasps against the corn borer

The parasitic wasps (Trichogramma) which are approx. 1 mm in size are so-called egg parasites. This means that they lay their eggs into the eggs of other parasites. In this case, into the eggs of the European corn borer. When the wasps hatch, the corn borer egg is destroyed, and the spreading of the harmful larvae is contained. The ichneumon wasps spread in the population, multiply and parasitise more corn borer eggs.

For a successful parasitisation by the ichneumon wasps, the right time of application of the beneficial insects is important. The start of the migration and the time of egg deposition are decisive. In order to choose the right time, official advisory institutions help to monitor the stages of the corn borer for different regions and give corresponding recommendations with regard to the application of the Trichogramma. 

Bringing the ichneumon wasps into the population

There are various methods and devices to do so. One of them is the application by means of small capsules.

Inside the capsules, there are ichneumon wasps in four different stages of development. After the capsules have landed on the surface of the population, the ichneumon wasps leave the capsules through a small slot. Afterwards, they start searching for the eggs of the corn borers. The different development stages guarantee that the control of the corn borer takes place over a longer period of time.

The capsules are made of maize starch or cellulose, so they are biodegradable. 

The capsules can be applied by hand or, in case of large areas, with drones or vehicles with sufficient ground clearance. For example, also with a distribution technology mounted on the boom of a Leeb self-propelled sprayer.

Important information about the corn borer and its control at a glance:

  • Most important pest in maize
  • Widespread all over the world
  • Causes yield and quality losses
  • Can be controlled chemically, mechanically or biologically

Ichneumon wasps as a natural method of control:

  • Prevent hatching of the harmful aphid larvae
  • The right time of application is important
  • Can be applied in small capsules