Journal of Agricultural Science; Vol. 14, No. 9; 2022 ISSN 1916-9752 E-ISSN 1916-9760 Published by Canadian Center of Science and Education 47 Residual Herbicides and Cover Crops Interactions for Soybean Weed Control Eduardo Roncatto 1 , Arthur Arrobas Martins Barroso 1 , Bruna Dal’Pizol Novello 1 , Renan Gonçalves 1 , Tiago Jarek 2 & Maurício Yung 2 1 Department of Phytotechnics and Plant Health, Federal University of Paraná, Curitiba, Brazil 2 Department of Agronomy, Pontifical Catholic University of Paraná, Curitiba, Brazil Correspondence: Eduardo Roncatto, Department of Phytotechnics and Plant Health, Federal University of Paraná, 1540 Funcionários St., Curitiba, Brazil. Tel: 55-46-99917-8683. E-mail: eduardo.roncatto@hotmail.com Received: June 19, 2022 Accepted: July 21, 2022 Online Published: August 15, 2022 doi:10.5539/jas.v14n9p47 URL: https://doi.org/10.5539/jas.v14n9p47 The research is financed by Coordination for the Improvement of Higher Education Personnel-Brazil (CAPES). Abstract Residual herbicides and cover crops are important tools inside an integrated weed management program. The straw produced in crop rotation can interacts with herbicides. The aim of this study was to evaluate the interaction of diclosulam, sulfentrazone, imazethapyr, flumioxazin, s-metolachlor and pyroxasulfone with black oat, cereal rye, common vetch and oilseed radish cover crops and it´s reflection on weed control and soybean production. Were evaluated the biomass production of cover crops and its influence on the soybean population. A phytosociological survey of the weed community was carried out, further evaluating the control provided by the herbicides and its effects on soybean productivity. Diclosulam was the more efficient herbicide tested, reducing both weed density and biomass (68% and 89%, respectively) compared to the fallow, independently of cover crop straw. The best control levels for the population identified were provided by the combination of the herbicides diclosulam with black oat, radish or fallow. We observed that herbicide efficacy in this case was more related with control spectrum than with herbicide-straw interation. This research demonstrates that the integration of cover crops and residual herbicides is efficient in the suppression and control of weeds in the soybean crop in the no-tillage system. Keywords: Black oat, diclosulam, pre-emergent herbicides, integrated weed management 1. Introduction Soybean (Glycine max (L.) Merr.) is a important oilseed for human and animal nutrition, with 37.03 million hectares being cultivated in Brazil with production of up to 126 million tons of grain, produced in more than 58% of the country’s arable area (Companhia Nacional de Abastecimento [CONAB], 2020). Is currently cultivated in the no-tillage system (NTS) which has as fundamental precepts the permanent vegetation cover and the seeding on the plant biomass of the predecessor crop. The success of the no-tillage system in tropical and subtropical environments is due to the cultivation of cover species combined with the use of the herbicide glyphosate for its desiccation (Day et al., 2020; Kan et al., 2020) The advent of transgenic RR (RoundUp Ready) soybean made it possible to control weeds also in crop post-emergence. However, the repeated use of the herbicide ended up selecting resistant weeds, which led to an increase of 149.14% in the use of herbicides between 2007 and 2014 in Brazil (Agrofit, 2020), in addition to the increase in environmental problems such as the drift of herbicides to non-target areas (Vieira et al., 2020). The worldwide demand for the production of food without specific patterns of chemical residues and the recent cases of limitation and prohibition of the use of glyphosate in countries in Europe and Latin America, also place Brazil at the center of the discussion on reducing the use of pesticides in food production on a global scale (Miyazaki, Bauer-Panskus, Bøhn, Reichenbecher, & Then, 2019). In this sense, the cultivation of cover species to maintain no-till also contributes to mitigating the use of herbicides. The establishment of cover crops is an excellent alternative for reducing the density and biomass