Condicionantes meteorológicos para a eficácia de controle de Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: noctuidae) em milho

Abstract

The maize crop (Zea mays) has great economic importance for Brazil, but the occurrence of the fall armyworm, Spodoptera frugiperda (J.E. Smith, 1797) (Lepidoptera: Noctuidae), can cause great losses in productivity, making use of plant protection products. In view of this reality, the main objective of this study was to determine the most favorable meteorological conditions to obtain maximum efficacy in insecticide applications in different spray volumes in the maize crop to control S. frugiperda. A field experiment was carried out with natural infestation of these insect pests on the maize crop, in Santa Maria, RS, during the 2018/2019 harvest. The treatments were arranged in a double factorial scheme with an additional 3 x 3 + 1 witness treatment, with two factors (time of application of treatments and spray volume) with 3 levels each (8AM, 2 and 6PM; 200, 300 and 400 L ha�����1), totaling 10 treatments. In the control treatment, no insecticide was applied. Evaluations of injury caused by S. frugiperda to the plant cartridge were performed using the visual scale of damage score (scale from 0 to 9), following the methodology described by Davis, Ng and Williams (1992). Analyzes of the characteristics of the spray droplets were also carried out using water-sensitive paper cards. The average values of the damage scores and characteristics of the drops of each treatment were submitted to the Scott-Knott test at 5 % probability. Atmospheric stability conditions were determined by analyzing the vertical profiles of the potential temperature. The results obtained showed that the meteorological condition present at the time of application of the treatments interfered with the effectiveness of controlling S. frugiperda in the maize crop. Generally speaking, the lowest values of damage scores were observed in applications that were carried out at 8AM, when the air temperature was lower and the relative humidity higher than at 2 and 6PM. The condition of stability that predominated in the first meters of the atmosphere was neutrality, with the exception of December 27, 2018 at 8AM, in which a stable layer was observed. In general, the greater spray volume generated greater diameter of spray drops.