European corn borer – the primary pest in corn crops
European corn borer (Ostrinia nubilalis) is one of the most economically important insect pests in corn, causing significant damage to corn plantations every year. According to the estimates of the Food and Agriculture Organization of the United Nations (FAO), European corn borer caterpillars are responsible for the destruction of approximately 4 percent of the total annual corn harvest worldwide. This is equivalent to the basic nutritional requirement of approximately 60 million people.
European corn borer – description
The European corn borer is a moth of the family Crambidae. It is yellowish brown in colour, and has a wingspan of approximately 3 cm. Males are generally smaller in size and darker in colour than females. Adults are mostly nocturnal moths, resting on corn plants during the day. Depending on the region, the first moths fly in from the previous year’s corn fields into the new crops from mid-June. In most cases, insect migration reaches its peak in July, but then continues well into August. Female moths fly in in the evening and at night, and lay their whitish egg masses on the lower leaf surfaces. Larger leaves in the middle of the plant are generally preferred for egg deposition. A typical cluster has 40 eggs from which yellowish caterpillars hatch within one or two weeks.
European corn borer – lifecycle
European corn borer larvae spread quickly and bore tunnels inside the stems and cobs. Broken corn panicles are an unmistakable sign of larval feeding. In places where the corn stalks are broken, a closer inspection reveals holes filled with a flour-like substance resulting from chewing tunnels, and larval droppings. Traces of their activity can also be found in the axilla of the lower leaves. Tunnels made inside the feeding tunnels may reach from the top to the base of the stalks, which may significantly reduce the stability of the plants, and adversely affect corn yields. Larvae may also eat their way inside the cobs, leaving holes and tunnels. (photo: damage caused by larval feeding (see the Markoldendorf field trial). However, ECB moths cause not only crop yield losses. Pest feeding sites also serve as access points for fungal spores, which use them as an opportunity to penetrate and grow inside the corn stalks. Moulds, including species forming extremely toxic metabolites (mycotoxins), are observed. An excessive level of mycotoxins leads to further deterioration of quality in corn plantations, and has a negative impact on the marketability of crops.
European corn borer – integrated pest management strategy
The first and most important element of the concept of European corn borer (ECB) management is mechanical fragmentation of crop stubble in corn fields in autumn. European corn borers overwinter as larvae in corn stubble fields. The fragmentation of crop stubble causes mechanical destruction of larvae on the one hand, and accelerates the rate of stubble decomposition on the other. Consequently, the larvae are prevented from going into winter hibernation. In addition, deep ploughing prevents the hatching of moths in May. Because ECB moths are mobile, and they actively fly into corn fields, it is crucial to ensure consistent mechanical control of the pests throughout the entire region.
Another element of the concept of ECB control is based on the use of Trichogramma wasps. Trichogramma wasps are a natural enemy of ECB moths. Being so-called egg parasitoids, Trichogramma wasps lay their eggs inside the eggs of the European corn borers, killing the developing larvae, as the parasitoid grows inside the host egg. Releasing large quantities of Trichogramma at an appropriate time results in the parasitisation of a large number of ECB eggs by females, approximately 0.5 mm in size, leading to egg destruction. This is why optimum application timing is so important. After the hatching of ECB larvae Trichogramma is no longer able to provide effective pest control. Here you can find more information about selecting optimum application timing.
In areas affected by Western corn rootworm, an insecticide is additionally used after Trichogramma application. Optimum application timing plays a key role in this scenario as well. The perfect solution is the application during the peak flight period of mature moths or during larval hatching. The use of insecticides, if needed, requires special technical solutions such as high-clearance tractors.