Chemical management of Phakopsora pachyrhizi: Effect on incidence, severity, and yield in soybean

Asian soybean rust (Phakopsora pachyrhizi) is one of the main diseases in soybean crops. In Mexico, there is limited knowledge regarding its management, therefore the objective of this research was to evaluate the effect of mixtures of fungicides of the families: Carboxamides, Strobilurins, and Triazoles on incidence, severity, fungicide efficiency, and yield in soybean variety ‘Huasteca 700’. Three commercial combinations of fungicides were evaluated: Tebuconazole + Trifloxystrobin, Fluxapyroxad + Pyraclostrobin, Cyproconazole + Azoxystrobin, with surfactant (Agrega®) at 0.1%, and a control which consisted only of surfactant. The highest incidence and severity occurred in the control treatment; fungicide application formulated with Strobilurins, and Triazoles significantly reduced incidence (54 to 98%) and severity (82 to 100%) and provided a crop protection period of 35 to 54 days post-application. The incidence and severity by stratum plant were lower in the second evaluation cycle, with respect the first evaluation. Damage remained below 1.24, 0.5, and 0.03% in the low, middle, and upper stratum, respectively in treatments treated with fungicides 56 days after the first application. With two applications of chemical fungicides formulated with Strobilurins and Triazoles, in a natural infestation of Asian soybean rust, the damage and incidence were significantly reduced compared to the control treatment.