1698 AJCS 13(10):1698-1705 (2019) ISSN:1835-2707 doi: 10.21475/ajcs.19.13.10.p1996 Spray volume deposits and fungicide efficacy on soybean rust (Phakopsora pachyrhizi) Evandro Pereira Prado 1 *, Carlos Gilberto Raetano 2 , Mario Henrique Ferreira do Amaral Dal Pogetto 2 , Rafael de Souza Christovam 2 , Paulo Renato Matos Lopes 1 , Rafael Simões Tomaz 1 , Pedro José Ferreira- Filho 3 , Diego Cunha Zied 1 , Julio Cesar Guerreiro 4 , Denise Tourino Rezende de Cerqueira 2 1 Sao Paulo State University/College of Technology and Agricultural Sciences, Rod. SP-294, km 651 - 17900-000 - Dracena, SP - Brazil 2 Sao Paulo State University/FCA − Dept. of Plant Protection, R. José Barbosa de Barros, 1780 − 18610 -307 − Botucatu, SP − Brazil 3 Department of Environmental Science, Federal University of São Carlos, 18052-780 - Sorocaba, SP - Brazil 4 Department of Agrarian Science, Maringá State University, 87502-970 - Umuarama, Paraná State, Brazil *Corresponding author: evandro.prado@unesp.br Abstract Soybean rust (SBR), caused by Phakopsora pachyrhizi, is one of the most destructive fungal diseases affecting soybean yields in many countries. Fungicide application methods that provide better SBR control efficacy may reduce soybean losses due to this disease. We investigated the effects of spray volumes applying the fungicide pyraclostrobin plus epoxiconazol at 133 + 50 g a.i. ha -1 by a conventional sprayer (CS) and an air-assisted sprayer (AAS). Field experiments were conducted comparing the effects of spray volumes of 110, 160, and 210 L ha -1 and two application techniques (CS and AAS) on spray deposits and SBR control. Fungicide efficacies were measured by disease severity, thousand seed weight, and yield. Correlations between disease severity and yield were also assessed. All treatments were applied with an Advance 2000 AM18 sprayer. In general, SBR disease and yield did not differ significantly when fungicide applications were applied with AAS compared to CS. Increasing the spray volume from 110 to 210 L ha -1 did not increase spray deposit coverage on soybean leaves. Low disease severity was obtained by fungicide applications using a spray volume of 210 L ha -1 . Safe recommendations of ground spray volumes for SBR control should be between 160 and 210 L ha -1 , using hydraulic nozzles. Keywords: Glycine max, pesticide application technology, spray deposits, spray rate. Abbreviations: SBR_Soybean rust; CS_conventional sprayer; AAS_air assisted sprayer; RH_relative humidity; ºC_degree Celsius; DLA_disease leaf area; AUDPC_area under the disease progress curve; TSW_thousand seed weight; ha_hectare; kg_kilogram; LSD_least significant difference; L:_liter; Rs_response ratio. Introduction Soybean [Glycine max (L.) Merrill] is an economically important crop cultivated by producers all over the world (Murithi et al., 2016). Soybean rust (SBR), caused by the fungus Phakopsora pachyrhizi Syd & P. Syd., is the most challenging disease of soybean in Brazil (Godoy et al., 2016). This is not only because the disease spreads rapidly, but also because it can cause significant yield reductions where management practices are poor (Prado et al., 2015). Despite many studies on the development of soybean cultivars resistant to P. pachyrhizi (Langenbach et al., 2016; Vuong et al., 2016; Childs et al. 2018), control has been difficult due to the variability and dynamic plasticity of the rust population, varying in virulence and genetic composition (Murithi et al., 2016). One of the most effective management strategies to suppress SBR severity and to reduce yield loss is the application of sequential fungicides (Scherm et al., 2009; Costa et al., 2015; Prado et al., 2015). The correct choice of fungicides, as well as many other parameters, is essential for satisfactory SBR control (Mueller et al., 2009). Optimal control of SBR is achieved with fungicides belonging to the triazole and quinone outside inhibitor (QoI) fungicide groups, particularly the combination triazole-QoI (Scherm et al., 2009; Mueller et al., 2009). Fungicides are typically diluted in water and distributed over crops in the form of liquid spray atomized by hydraulic nozzles. The purpose of pesticide applications is to reach the target and to obtain coverage, resulting in the optimal efficacy of the applied product (Jensen and Olesen, 2014), while at the same time avoiding pesticide losses by drift. Symptoms associated with SBR are initially observed in the lower soybean canopy and then move upwards as the disease progresses (Zhu et al., 2008). To provide fungicide coverage on the leaves in the lower canopy is not an easy task, especially in dense canopies. Air-assisted spraying (AAS) is a technique that may improve droplet penetration and increase the amount of coverage of the lower canopy