After records in recent harvests, it is estimated that in 2024 Brazil should harvest around 116.9 million tons of corn, according to IBGE. To achieve good productivity, it is necessary to pay attention to some management, as the crop can suffer pest attacks from sowing to harvest. Therefore, production can be compromised if adequate management and monitoring are not carried out throughout the entire development of the crop.
Pests can damage both the aerial part and the root system of plants, with the highest incidence at the end of the corn cycle being the caterpillars Spodoptera frugiperda and Helicoverpa zea, and the aphid Rhopalosiphum maidis.
- Fall armyworm (Spodoptera frugiperda)
One of the most important pests with potential damage to corn crops is the fall armyworm (Spodoptera frugiperda). It can present morphological characteristics such as brown, greenish or black coloration, with its main characteristic being the presence of an inverted “Y” on the head, which characterizes its field monitoring (Figure 1).
In its initial phase, it attacks corn seedlings and feeds on them, reducing the plant population. The caterpillars feed on the leaves by scraping them and, later, from the second or third instar onwards, they make holes in the leaves towards the plant cartridge. Before the plant emits the tassel, this caterpillar can also feed on the grains from the cob, even causing total loss of production of the attacked plant. Furthermore, it can cause indirect damage to the cob, such as, for example, favoring the incidence of fungi and bacteria.
To avoid this pest in crops, the application of insecticides can be applied before sowing the corn, along with desiccation, in addition to investing in resistant hybrids and carrying out seed treatments that control this pest. To control the fall armyworm, carbamate insecticides, chitin synthesis inhibitors, spinosyns, organophosphates and pyrethroids can be used. In addition to these, there is the possibility of carrying out control using biological insecticides based on the baculovirus of the bacteria Bacillus thuringiensis, and the parasitoid Trichogramma.
If adequate management and control are not carried out, production can be reduced by 50% in areas with a high population of this millta.
Earworm (Helicoverpa zea)
According to data from Embrapa (2008), it is stated that the importance of the pest for corn crops can be verified with an average reported incidence of up to 96.8% of infestation, since infestations by H. zea are frequent and cause damage expressive,
With the attack of the earworm (Figure 3), in addition to its direct damage consuming the forming grains, the indirect damage is also significant and results in the lack of formation of second ears, absence of fertilization of a large part of the ovules of the late ears, as well as failure of grain fertilization at the tip of the ears.
The morphology of this pest is characterized by adults that are a moth with yellow-brown forewings, and a darker transverse stripe, also presenting dark spots scattered over the wings. During periods of higher temperature and longer days, in three to four days, the caterpillars hatch and begin feeding immediately. As they develop, they penetrate the interior of the cob and begin to destroy the forming grains.
As with the fall armyworm, it is important to use resistant cultivars, due to the difficult access of the chemical insecticide inside the ear to control the pest. Among the recommendations, one of the alternatives is the application of toxic bait so that the moths are killed before laying eggs.
Corn aphid (Rhopalosiphum maidis)
The corn aphid (Figure 4) is a sap-sucking insect that feeds by introducing its mouthparts into the young leaves of plants. The adult is bluish-green in color. In general, it is considered a secondary pest in corn intended for grain, but it is of fundamental importance in seed production fields, where control levels are more severe. Dry periods can favor increases in the pest population and, consequently, damage to the host plant. In corn, Embrapa (2008) found that the adult's life span was 20 days, considering a temperature of 24°C.
The management of this pest, even with aerial spraying, is unsatisfactory due to the occurrence of this insect at the end of the vegetative stage and beginning of the reproductive stage, that is, the crop already has closed inter-rows. However, systemic insecticides can be used to control the aphid, due to the translocation of the insecticide through the plant.
Faced with the damage caused by these pests, Integrated Pest Management (IPM) is an efficient strategy, as it aims at frequent monitoring of insects, natural control and assesses the level of tolerance of plants to the infestation. These factors contribute to more assertive decision-making, evaluating what, how much and when to apply. Therefore, these control strategies are essential to protect corn productivity potential in cases where these pests are present.
Text written by Gabriela de Azevedo Martins and Lidiane Bilibio Bonfada, members of AGR Jr. Consultoria Agronômica, Junior Company of the Agronomy Course at UFSM Campus Frederico Westphalen, under the guidance of professor Dr. Gizelli Moiano de Paula.
