CHEMICAL CONTROL OF ASIAN SOYBEAN RUST AS A FUNCTION OF CULTIVAR, ROW SPACING AND SPRAY BAR SUPPORT SYSTEMS

ABSTRACT Product deposition and foliar surface cover are highly impacting factors on the efficiency of foliar fungicides applied to soybean cultivars, due to their low mobility, with side effects on Asian soybean rust (ASR) control. Spray bar support systems, such as the air curtain (Vortex®) and the use of nozzles along the bar (Dropleg®), stand out as an alternative to obtain a better distribution of fungicide throughout the plant. In this study, two spray bar support systems (Vortex® and Dropleg®) were, therefore, evaluated and compared with the conventional spraying method based on the biological efficacy in ASR control. In order to do this, two harvests, with three spacing between rows and two cultivars were employed. Vortex® and Dropleg® spray bar support mechanisms do not effectively contribute to the optimization of Asian soybean rust control or to the grain crop yield, regardless of cultivar and row spacing. Decreasing the row spacing did not influence the level of control of Asian soybean rust, as the highest grain yield was obtained with the smallest spacing. The cultivar with genetic resistance to Asian rust showed lower levels of this disease, thus, greater control against the use of fungicides.