“In the last season, pesticide use represented 8.96% of production costs. Intensity of pest and disease attacks across the country contributed to increasing costs of production and difficulty in managing the crop.”
Aline Vanessa Sauer is an agronomist from the Northern Paraná State University (UENP), has a master’s degree in plant protection/phytopathology from State University of Londrina and a PhD in the same area from State University of Maringá. Sauer is a professor in the agronomy course and in the master’s program in agronomy at UENP.
Corn cultivation has undergone several changes in recent years, with the help of genetic improvement. Among them is the advancement of areas and growing seasons. Continuous presence of plants in the field changed the initial scenario from a species considered rustic to a crop where phytosanitary problems arise frequently. Among the main problems that affect corn cultivation, diseases stand out as responsible for up to 80% of yield losses.
Corn white spot, caused by the bacterium Pantoea ananatis, is corn’s main foliar disease. Bacteria can survive in plant residues and in weeds such as Digitaria insularis and D. horizontalis, popularly known as sourgrass and Jamaican crabgrass, respectively. In addition to these plants functioning as a source of inoculum, herbicide resistance frequently reported for D. insularis makes it difficult to manage the disease in the field. Recently, a research group in the USA confirmed the transmission of the bacteria that causes white spot by a species of Diabrotica spp. that still does not occur in Brazil.
Corn stunt disease (pale and red stunting) is caused by a group of bacteria known as mollicutes. Stunting is a systemic disease with an infectious process that occurs in the phloem tissues of plants. Transmission occurs by the corn leafhopper Dalbulus maidis and has a high potential for damage. Damages range from yield losses resulting from malformation of the corn ears to the damping off and premature death of plants.
Other diseases have also gained prominence in recent harvests. Helminthsporiosis, caused by the fungus Exserohilum turcicum, can cause losses of 50% if it occurs before flowering. The symptoms are leaf spots that range from 2.5 to 15 cm in length and are easily confused with symptoms of other diseases by professionals and farmers.
Diplodia leaf spot is caused by the fungus Diplodia macrospora and can affect both leaves and ears. On leaves, symptoms consist of elongated lesions ranging from 1.5 to 25 cm in length.
Brown eye spot is caused by the fungus Cercospora zea-maydis and can reduce production causing severe losses. Symptoms consist of small leaf lesions, 1 to 6 cm long, that accompany the leaf veins and are observed especially during flowering.
To differentiate the phytopathogenic agents that affect corn and to reach the correct diagnosis, it is necessary to pay attention to some details in the symptoms. In brown eye spot, lesions are smaller and always respect the leaf veins. In helminthosporiosis, lesions are larger and do not respect the leaf veins, as with Diplodia spot. However, in the case of Diploidia, spots are narrower and always demonstrate the initial point of infection.
In the last season, pesticide use represented 8.96% of production costs. Intensity of pest and disease attacks across the country contributed to increasing costs of production and difficulty in managing the crop.”