Temporal dynamics of Asian soybean rust according to sowing date and fungicide application, and its effects on soybean yield in the Northwest Mesoregion, Rio Grande do Sul, Brazil

Asian soybean rust (Phakopsora pachyrhizi) is one of the most serious diseases threatening soybean yields in Brazil. Practices such as sowing season scheduling in conjunction with fungicide application may interfere with disease development and crop impact. The aim of this research was to assess the progress of Asian soybean rust and soybean yield based on different sowing dates, combined with or without fungicide application. The soybean cultivar 'DM 53i54 RSF IPRO' (susceptible to Asian soybean rust) was sown in a split-plot design during the 2017/2018 and 2018/2019 crop seasons, with the main plot having sowing date (October, November, December, and January), and the subplot being fungicide application (presence or absence). The temporal dynamics of the disease were obtained based on severity (%), and the area under the disease progression curve. Additionally, number of pods per plant, thousand grain weight, and yield were all assessed. The disease progressed exponentially. The use of fungicide reduced disease severity across all crop seasons and sowing dates. The delay in the sowing date resulted in greater disease severity and a better effect of the fungicide. Soybean yield, number of pods per plant, and thousand grains weight were all higher in October and November than in December and January. Anticipation of sowing, in October, in conjunction with fungicide application reduced Asian soybean rust damage and increased soybean yield, mainly in crop seasons with high disease inoculum pressure. © 2023, Indian Phytopathological Society.