Mixing Elemental Sulfur or Chlorothalonil with QoI and DMI Fungicides for Management of Late Leaf Spot of Peanut

Reduced sensitivity to demethylation inhibitor (DMI) and quinone outside inhibitor (QoI) fungicides in <i>Nothopassalora personata</i>, the cause of late leaf spot of peanut (<i>Arachis hypogaea</i>), complicates management of this disease in the Southeastern United States. Mixtures with protectant fungicides may help preserve the use of members of both DMI and QoI fungicide groups for leaf spot management. Field experiments were conducted in Tifton, GA, from 2019 to 2021 and in Plains, GA, during 2019 and 2020. The primary objective was to determine the effects of mixtures of DMI fungicides tebuconazole and mefentrifluconazole and QoI fungicides azoxystrobin and pyraclostrobin with micronized elemental sulfur on late leaf spot in fields with populations of <i>N. personata</i> with suspected reduced sensitivity to DMI and QoI fungicides. In four of the experiments, the efficacies of elemental sulfur and chlorothalonil as mixing partners were also compared. In most cases, standardized area under the disease progress curve (sAUDPC) and final percentage defoliation were less for all DMI and QoI fungicides mixed with sulfur or chlorothalonil than for the respective fungicides alone. In most cases, sAUDPC and final percentage defoliation were similar for sulfur and chlorothalonil when mixed with the respective DMI or QoI fungicide. These results indicate that mixtures of DMI or QoI fungicides with either micronized sulfur or chlorothalonil can improve control of late leaf spot compared with the DMI or QoI fungicide alone. These results also indicate that elemental sulfur has potential as an alternative to chlorothalonil in tank mixes where that protectant fungicide is currently being used as a mixing partner to improve leaf spot control.