Impact of defoliation at the reproductive stage in different leaves of the soybean plant

Abstract

Inadequate phytosanitary management can cause a significant reduction in the leaf area of soybean, which directly impacts its yield. The aim of this study was to evaluate the impact of defoliation in the lower, middle and upper leaves of the canopy, at three reproductive stages, on soybean yield, as a tool for improving phytosanitary management. The design was randomized blocks in 3x3+1 factorial scheme, with 4 replicates. The 10 treatments resulted from the combination of 3 defoliation positions on the plant (lower, middle and upper leaves) and 3 phenological stages of the crop (R1, R3 and R5), in addition to a control without defoliation. Morphological and production components and grain yield were evaluated. The data were subjected to analysis of variance and, when a significant difference was identified, the means were subjected to the Dunnett test. It was observed that plants showed a reduction in height in treatments with defoliation in the upper leaves at R1 and R3 stages. For the variables thousand-grain weight and grain yield there was difference only when defoliation was performed at the R5 stage in the upper leaves, resulting in a 16.6% loss in grain yield compared to the control. The soybean crop tolerates a defoliation level of 33.3% up to the R4 stage, in any of the leaves, without significant reduction in grain yield. Upper leaves, from the R5 stage, should be prioritized in the applications of phytosanitary products, which aim to reduce the damage caused by defoliation.