Relações lineares entre variáveis no controle de buva em soja com diferentes manejos hibernais

Abstract

Brazil is considered the world largest producer of soybeans (Glycine max (L.) Merril). Due to its importance, weed control, such as hairy fleabane (Conyza spp.) should be prioritized, once cases of resistance to the herbicide glyphosate make its control more difficult, requiring new tools to be implemented, such as control cultural associated with the chemical during the off-season. These relationships have not yet been studied from the linear relationships. Therefore, the objective of this study was to evaluate the effects of the integration of cultural and chemical control methods on the hairy fleabane population and its effects on soybean yield using linear relationships. The experiment was conducted at the Federal University of Santa Maria with four replications, during three soybeans crop season: 2018/19, 2019/20 and 2020/21. Cover crop factors (white oat, Ukrainian oat, ryegrass, rye and fallow) and herbicides (2,4-D, metsulfuron-methyl, metribuzin, saflufenacil and control) were used as treatments. The following variables were quantified: hairy fleabane population at stage Z24 and Z29 of cover crops, pre-sowing and soybean V4 and R5 stages, hairy fleabane dry mass, cover crop dry mass, phytotoxicity of herbicides on cover crops, visual control of hairy fleabane, number of soybean plants, soybean plant height, thousand grain weight and soybean yield. Data were submitted to Pearson's linear correlation analysis, cause and effect analysis, Scott-Knott test (p<0.05) and canonical correlation analysis. Hairy fleabane population is negatively correlated with cover crop dry mass and soybean yield. Hairy fleabane population at stage V4 and hairy fleabane dry mass were the variables that contributed to the association of the others on soybean yield, while hairy fleabane population at stage R5 contributed both indirectly and directly. The hairy fleabane population at soybean pre-sowing and control at 28 days after herbicide application contributed to the indirect effects on the hairy fleabane population at soybean R5 stage, while the cover crop dry mass showed direct effects, evidencing the cultural control. In general, the effects provided by integrated management on soybean yield are highlighted, once cover crops associated or not with herbicides were efficient in controlling the hairy fleabane population, equaling fallow only when using the saflufenacil herbicide. The metsulfuron-methyl herbicide showed control failures on hairy fleabane. These associations were confirmed by the existing relationship between the groups related to the management of hairy fleabane and the soybean crop. We concluded that the ideal time to control this weed during the off season and that the maintenance of cover crops becomes essential in the management of this weed, because grass cultures allow the use of herbicides that provide increments in hairy fleabane control.