Author: Doc. dr Miloš Petrović, Faculty of Agriculture, University of Novi Sad
Corn is one of the most important agricultural crops. Many cultures worldwide depend on it, as it is used as a primary source of food. The production of corn is one of the most technologically advanced, mostly because corn in the first vegetative stages of development is highly dependent on farmers’ hard work. Weeds are often referred to as a main problem, especially during the development of the first 9 to 10 leaves. What is interesting is that, from the ecological perspective with the special emphasis on entomofauna, corn fields are beginning to bloom after that “pampering” period.
Navigating the Pest Predicament: Insects’ Impact on Corn Farming
Corn fields are often rich both in benefits and, more importantly, in insect pest fauna. Every vegetative and generative part of corn attracts many insects belonging to different insect orders. At first glance, mention of butterflies is often associated with insects rich in color and gracious but in the case of corn the situation is not so idyllic. The European corn borer Ostrinia nubilalis and cotton/corn bollworm Helicoverpa armigera are one of the species from order Lepidoptera responsible for more than 80% damage on corn stalks as well as the ears of corn.
European corn borer, a species from the family Pyrallidae has two to three generations during the vegetative year, and the first two generations being the most dangerous for corn production. The first generation is present in the fields from the middle of May until the later weeks of June.
After the pairing (coppulation) females often lay the distinctive egg mass on the downside of the leaves. During the embryogenesis egg mass changes color from white to milky white, to coffee brown with characteristic dark dots. Young caterpillars have interesting behavior after hatching called “wandering” – phenomena during which the larvae try to find perfect spots on corn plants for feeding. The first two or three instars – stages of development feed on leaves, and after that, caterpillars start to burrow themselves inside the corn stalk – and that is the time when problems start!
Eating the inside of the stalk, the corn plant becomes extremely unstable, and these damages are making them prone to breaking during the heavy weather conditions (heavy rain accompanied by a strong wind). Unfortunately for farmers, problems with this species do not stop in June, because the second generation is becoming present during late July and early August together with another species which belongs to another family – Noctuidae. Helicoverpa armigera and O. nubalilis are usually found together in the fields, and sometimes even in the same plant. This time, the main damages are occuring on corn ear, where caterpillars have feeding frenzy zone, because they are feeding on seeds rich both in protein and carbohydrates. The tip of the corn ear is often the main place where caterpillars are starting their feeding journey, and this spot often has a distinctive look – symptom. Because of their habits to burrow inside the corn ear, the tip looks like mini vulcano, but this time the lava is not coming out, the insect faeces is what makes it look like this. This damage makes it double trouble. The first damage is the direct one, because the eaten seeds are directly affecting the yield per hectare. The second one, in some years, is even more important. The holes and crevices which caterpillars make are opening sites for many microorganisms, some of which can make a huge problem. Species of fungi from genus Penicillium, Aspergillus and Fusarium are a dangerous trio, who use the opening sites as a starting point of the infestation. Occupying the corn seeds, they start to make a suitable niche for themself by producing notorious mycotoxins. These semio-chemicals are one of the most dangerous naturally produced products, as they pose potent cell penetrating agents, which consequently can make cell deformations, and genomyc mutations.