Comparing The Effects of Sulfur-Synthetic Fungicide Mixtures On Leaf Spot And Rust Peanut Pathogens
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Authors
Taylor, Kenyanna
Issue Date
2024-02-21
Type
Thesis
Language
en_US
Keywords
Academic theses , Biology , Epidemiology , Plant diseases , Defoliation , Peanut industry , Peanuts--Diseases and pests , Fungicides , Leaf spots
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Abstract
Early and late leaf spot, caused by the fungi Passalora arachidicola and Nothopassalora personata, are important foliar diseases of peanut that can lead to premature defoliation and yield loss if not controlled. In fields with a history of leaf spot, the diseases are managed using frequent applications of fungicides. Recently, mixtures of micronized elemental sulfur with tebuconazole, a demethylation inhibitor (DMI) fungicide, or azoxystrobin, a quinone outside inhibitor (QOI) fungicide, were shown to lessen defoliation caused by leaf spot. The objective of this study was to determine if sulfur mixtures reduce defoliation by causing fewer leaf spot infections or by increasing plant tolerance. Field studies conducted at the University of Georgia Coastal Plain Experiment Station in 2020 and 2021 exposed peanut plants to 7 applications of six fungicide treatments at recommended rates: (1) a nontreated control, (2) sulfur, (3) tebuconazole (DMI), (4) DMI + sulfur, (5) axozystrobin (QoI), and (6) QoI + sulfur. Disease was assessed weekly between 90 and 140 days after plating (dap) using the FL 1-10 scale, a visual estimation of defoliation and disease severity, and as the number of leaflets with leaf spot (leaflet incidence) and the mean number of lesions per leaflet (leaflet severity) for 10 lateral branches per plot. As expected, defoliation assessments were significantly lower for the sulfur mixture treatments than the DMI and QoI treatments alone in most cases (P<0.05). A similar pattern was observed for leaflet incidence and leaflet severity (P<0.05). There was a significant exponential relationship between cumulative leaflet severity (AUDPC severity) and final defoliation (R2 = 0.77; P<0.001) and AUDPC severity and AUDPC defoliation (R2 = 0.82; P<0.001). In most cases, sulfur effects on defoliation were insignificant when AUDPC severity was included as a covariate in the model (P>0.05). This suggests that the mechanism of reduced defoliation is due to fewer leaf spot infections rather than increased plant tolerance.
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