Effect of DMI and QoI fungicides mixed with the SDHI fungicide penthiopyrad on late leaf spot of peanut

In recent years, succinate dehydrogenase inhibiting (SDHI) fungicides have become important for control of early leaf spot (Passalora arachidicola) and late leaf spot (Nothopassalora personata) of peanut (Arachis hypogaea) in the southeastern U.S. In this study, pyraclostrobin, cyproconazole, and thiophanate-methyl were compared for efficacy alone and as mixing partners with SDHI fungicide penthiopyrad for control of late leaf spot. In all trials, mixtures of penthiopyrad + pyraclostrobin or penthiopyrad + cyproconazole improved leaf spot control compared to penthiopyrad alone based final percent defoliation, and in most cases based on area under the defoliation progress curve. Additional control provided by mixtures with thiophanate-methyl was minimal compared to penthiopyrad alone. In trials at Tifton and Plains, GA, efficacies of the mixtures of penthiopyrad + cyproconazole and penthiopyrad + pyraclostrobin were greater than expected based on performance of the respective individual fungicides, indicating synergistic effects of these fungicide combinations.