Glufosinate and diquat in pre-harvest desiccation of soybean at four phenological stages, and their impact on seed quality

ABSTRACT Glufosinate and diquat may have different levels of efficacy in the pre-harvest desiccation of soybean (Glycine max (L.) Merr.) plants, and may affect quality of seeds differently, depending on the phenological stage at which they are applied. The objective of this study was to evaluate desiccation with glufosinate and diquat at the phenological stages R6, R7.1, R7.2, and R7.3, and to examine their effects on yield and quality of soybean seeds. The experiment was conducted at two sites in the state of Paraná (PR), Brazil, in the 2020-2021 crop season. A randomized block design was used, treatment groups consisted of application of glufosinate or diquat at R6, R7.1, R7.2, and R7.3, and the control group (without desiccant application). Defoliation, maturity, moisture, yield, and seed quality (vigor and germination) were evaluated. Glufosinate and diquat were effective at desiccation and had a significant effect on defoliation and maturity, with final values ≥ 98.8% and ≥ 99.3% respectively. Treatments can accelerate harvest maturity by approximately 3 d and earlier applications do not necessarily favor this acceleration, most notably in trial 1. However, desiccation at earlier stages reduced seed yield and negatively affected seed quality, with values of only 61.3% and 71.8% of vigor and germination in some situations. The application of glufosinate or diquat was effective in the pre-harvest desiccation of soybean plants, with no differences between the assessed herbicides or phenological stages. The application of glufosinate starting at R7.2 or diquat at R7.3 is ideal to avoid deleterious effects on seed yield. Applications at earlier stages may lead to losses of more than 30% seed yield. The use of diquat or glufosinate before R7.2 may reduce the quality of seeds.