Masters Theses

Date of Award

8-2025

Degree Type

Thesis

Degree Name

Master of Science

Major

Entomology and Plant Pathology

Major Professor

Heather Kelly

Committee Members

Sebe Brown, Jake McNeil

Abstract

United States soybean growers routinely use fungicides to control the spread of foliar diseases such as frogeye leaf spot, Septoria brown spot, and target spot. Research indicates that fungicide classes such as QoI, DMI, and SDHI, in addition to controlling fungal disease outbreaks, have the potential to improve plant performance when under environmental stress, notably water deficit stress. The goal of this study was to evaluate the impact of Miravis Top’s (pydiflumetofen and difenoconazole) on physiological parameters in soybean and its potential in mitigating drought stress in both controlled environments and field trials. In controlled environment experiments, a total of three soybean varieties were treated with Miravis Top (13.7 fl. oz/acre[MJ1] , 1.0 L/ha) (pydiflumetofen 6.9% a.i., difenoconazole 11.5% a.i.), combined with nonionic surfactant (0.25 v/v) at four weeks after planting (V4-V6) and monitored for changes in transpiration rates under progressive soil drying conditions in a greenhouse, and vapor pressure deficit (VPD) stress in controlled temperature and humidity chambers. In field trials, the same Miravis Top application was made at approximately theR3 growth stage (beginning pod development) at three different locations with three levels of water availability: irrigated, rain fed, and rain-out sheltered. Relative water content (RWC) and stomatal conductance were evaluated immediately before fungicide application, three days after application, and then every seven days until twenty-eight days after application was reached. Fungicide application did not improve overall soybean response to environmental stress in either of the controlled environment trials. In field trials, RWC of fungicide treated plots was higher than non-treated plots 3 days after application, but only at one location. 24 days after fungicide application, stomatal conductance of treated plots exceeded that of non-treated plots at one location, but stomatal conductance of once treated plots exceeded those of twice treated plots at another location at the same time. Yields of treated and non-treated plots were not significantly different in any growing season. Yields of twice treated plots exceeded those of once treated plots in 2023, while the opposite was true in 2024.

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