Avaliação da produtividade da soja em relação a severidade do oídio no momento da aplicação do fungicida

Abstract

The occurrence of powdery mildew (textitMicrosphaera diffusa Cke. & Pk.) in soybeans (textitGlycine max (L.) Merr.), can cause high productivity losses, especially when environmental conditions are conducive to the development of the disease. Currently it is possible to visualize in the field changes in the behavior of the disease, characterized by the increasing difficulty of control and greater damage in production, increasing the number of applications for the control of powdery mildew and the cost of grain production. The high number of fungicide applications can be explained by the lack of information about the correct time for powdery mildew control. Therefore, information was generated for farmers, agricultural technicians, agronomists and the scientific community for the proper positioning of fungicides in the chemical control powdery mildew in soybean, contributing to the reduction in the number of fungicide applications, maintaining grain productivity and reducing costs. To establish the correct moment of fungicide application, the severity index powdery mildew was identified, which will cause economic damage in soybean crop. Five treatments were performed in which the following criteria were followed, in the first treatment the fungicide was performed before the soybean crop presented the first symptoms powdery mildew, in the second treatment the fungicide application occurred at the time reached 15% of powdery mildew severity, in the third treatment the fungicide application occurred at 30% of powdery mildew severity, in the fourth treatment, fungicide application occurred at 45% of powdery mildew severity and in the fifth treatment fungicide application occurred at 60% of powdery mildew severity. The experiment with the soybean cultivar BMX RAIO 50152 RSF IPRO was conducted in a randomized block design, with five treatments and four replications, totaling twenty plots. The data obtained from the evaluations of disease severity and productivity were submitted to variance analysis at a level of 5% probability of error, followed by polynomial regression analysis. As a result, it was observed that the application of fungicide in the percentage of 15% of leaf area affected by powdery mildew was the one that presented the best field result in relation to productivity, resulting in 72.26 bags ha−1. On the other hand, the point of maximum technical efficiency determined that the application of fungicide in the severity of 6.25% is the one that results in the maximum productivity of soybean, being 69.83 bags ha−1. Establishing the appropriate time for the application of fungicide for the control of powdery mildew allows the farmer to reduce the cost of fungicides, with the cost of applications and the damage caused to the environment by the use of chemicals. The evaluated data were submitted to variance analysis at a level of 5% probability of error, followed by polynomial regression analysis.