Combinations of elemental sulfur with demethylation inhibitor fungicides for management of late leaf spot (Nothopassalora personata) of peanut

Abstract

Management of demethylation inhibitor (DMI) fungicide resistance in Nothopassalora personata, the cause of late spot of peanut (Arachis hypogaea), is a challenge in peanut production areas of the southeastern United States. Field experiments were conducted in Tifton, GA in 2017 and 2018, and in Plains, GA and Blackville, SC in 2018 to determine the effects of mixtures of micronized elemental sulfur with DMI fungicides, cyproconazole, and a premixture of prothioconazole plus tebuconazole on late leaf spot in fields with DMI-resistant populations of N. personata. Application of sulfur alone provided little reduction in final levels of defoliation compared to the nontreated control. However, mixtures of elemental sulfur with either cyproconazole or the premix of prothioconazole + tebuconazole provided the control that was superior to either of the DMI treatments alone. Greater than additive effects on final leaf spot severity were observed in all trials for mixtures of one or both of the DMI fungicide treatments and sulfur. Greater than additive effects on standardized area under the defoliation progress curve were observed for both DMI fungicide treatments with sulfur in trials at Tifton and Plains, GA. The results suggest that the addition of micronized elemental sulfur to DMI fungicides has potential to improve leaf spot control in fields where the efficacy of DMI fungicides alone is not adequate.