Pre- and postinfection application of strobilurin-triazole premixes and single fungicides for control of fusarium head blight and deoxynivalenol mycotoxin in wheat

Fungicide application is considered a valid management strategy for fusarium head blight (FHB) in wheat and deoxynivalenol (DON) accumulation in grain. Its efficacy, however, varies greatly depending on the severity of the epidemic, cultivar resistance, fungicide type, timing of fungicide application, and application technology. In subtropical, humid, southern Brazil, premixes containing both a strobilurin and a triazole fungicide have been considered an option for application at flowering stages when, in addition to FHB control, it is desirable to have more efficacy in the control of leaf diseases; however, the impact of these fungicide mixtures on the accumulation of DON in the grain is not fully understood. This study examined the pre- and postinfection activities of strobilurin-triazole premixes, as well as single triazoles, strobilurins and a benzimidazole fungicide, on controlling FHB and reducing DON accumulation in wheat. The experiments were conducted in four growing seasons under artificially induced severe epidemics. It was verified that the type of fungicide and the timing of application influenced both the FHB control and reduction of contamination by DON. In both pre- and postinfection application, the triazole fungicides metconazole, tebuconazole, and propiconazole, as well as the benzimidazole carbendazim, presented greater constancy over the four growing seasons in reducing DON than did the strobilurin-triazole premixes trifloxystrobin+prothioconazole, trifloxystrobin+tebuconazole, pyraclostrobin+metconazole, and azoxystrobin+cyproconazole. On the other hand, the premixes, except the last one, and the triazole and benzimidazole fungicides provided 70% or more FHB control in preinfection application across seasons. Overall, FHB control levels were higher in preinfection than in postinfection application. The results indicated that, even though the strobilurin-triazole premixes or the strobilurins alone provide satisfactory FHB control, their impact on DON reduction may be uncertain, suggesting the need for caution in their use. Such information is expected to help farmers make better decisions regarding fungicide choice for FHB and DON management.