Evaluation of the efficacy and application timing of different fungicides for management of soybean foliar diseases in northwestern Argentina

Diseases are among the main factors that reduce soybean yields in Tucumán and other provinces in northwestern Argentina. The main diseases that affect the foliage of soybean plants in this region are target spot (caused by Corynespora cassiicola ), Cercospora leaf blight ( Cercospora kikuchii ), and Asian soybean rust ( Phakopsora pachyrhizi ). The objective of this work was to evaluate the efficacy and application timing of different chemical fungicides for the management of these diseases in northwestern Argentina. Field trials were conducted during three growing seasons (2014/2015, 2015/2016, and 2016/2017). The fungicide treatments that presented statistical differences ( P < 0.05) for target spot control compared to the untreated control in all growing seasons were those that included pyraclostrobin + epoxiconazole + fluxapyroxad (applied at R3, R5 and R3 + R5) and pyraclostrobin + epoxiconazole and azoxystrobin + cyproconazole at R3. For Cercospora leaf blight control, all treatments differed statistically from the untreated control in the 2014/2015 crop season, except for azoxystrobin + cyproconazole and azoxystrobin + benzovindiflupyr applied at R3 and pyraclostrobin + epoxiconazole at R5. Only azoxystrobin + cyproconazole at R3 in 2015/2016 and all the fungicide treatments in 2016/2017 differed statistically from the untreated controls. Soybean rust severity at R6 was low, 1.0% and 3.0% in the untreated control during 2014/2015 and 2015/2016, respectively, but increased to 54.2% in 2016/2017. Treatments that showed the lowest soybean rust severity values in the latter season were pyraclostrobin + epoxiconazole + fluxapyroxad (R3 + R5 and R5, with 17.4 and 17.1%, respectively), and azoxystrobin + benzovindiflupyr (R3 and R5, with 20.2 and 15.0%, respectively). Overall in this season, the efficacy of each fungicide for ASR control was better when applied at R5 than at R3. The treatments pyraclostrobin + epoxiconazole + fluxapyroxad applied at R3, R5 and R3+ R5 and treatments azoxystrobin + benzovindiflupyr and pyraclostrobin + epoxiconazole at R5 yielded significantly higher than the untreated control during all three seasons. These results should help improve management of soybean foliar diseases in northwestern Argentina. • Target spot, Cercospora leaf blight, and soybean rust are important soybean diseases. • We evaluated efficacy and application timing of fungicides for their control. • For each disease we determined the best fungicide treatment and moment of application. • Results obtained will improve soybean disease management in northwestern Argentina.