Damage Pattern
The first signs of infestation are rows of feeding holes in the middle and upper leaves. Infestation at the stem is marked by the appearance of boreholes. The upper stem section often bends with a "flag," and the plants may bend below the cob, disturbing nutrient storage in the cob. The cob can also be penetrated by the larvae's feeding tunnels, especially at the base and rachis. If the grains are still soft, larvae can also penetrate the cob from the outside. The feeding sites are also ideal entry points for fungi, such as stalk and cob rot or corn smut.
Biology and Temporal Occurrence
The larvae of the European corn borer are yellowish or reddish-brown, up to 3 cm long, with a black head capsule. The adult moth is 12-15 mm long with a wingspan of about 30 mm. The moths typically fly into the maize fields between June and July. The female lays up to 40 eggs in several clutches on the underside of the central corn leaves. The larvae hatch after 14 days, feed through the plant, and overwinter in maize stubble. In Germany, the European corn borer is found mainly in the southern regions and, more recently, in the Rhineland and Western Pomerania.
Damage Threshold
The damage threshold for the European corn borer is 10-15 eggs per 100 maize plants. Local recommendations should be followed for control, as the infestation and optimal control timing are difficult to assess.
Control
Mechanical Control
Shred stubble residues and incorporate them thoroughly (plowing) after harvest. Field hygiene and a collaborative approach are important.
Biological Control
Use of Bacillus thuringiensis: This bacterium, when sprayed on the plant surface, multiplies in the insect's gut and produces toxins, killing the moth.
Use of the parasitic wasp Trichogramma evanescens: This egg parasite lays its eggs in the moth's egg clutches. The larvae eat the eggs, pupate, and eventually emerge as new wasps. Parasitized eggs are typically released using drones.
Chemical Control
Chemical control is also possible, best applied at the peak of moth flight. Once larvae have entered the plant, chemical control is ineffective. Special application technology is required.