P-407 - Effect of Light on the Efficacy of Foliar Fungicides for Managing Frogeye Leaf Spot in Soybean

Foliar fungicides are traditionally applied using ground or aerial equipment, but drones are increasingly used, sometimes at night. It remains unclear if nighttime applications of foliar fungicides affect their efficacy due to differences in environmental and physiological factors. This study assessed the effect of light exposure and fungicide application on disease development in a controlled condition using a two-factorial randomized complete block design with six replications. The first factor was light exposure (six hours of light vs. complete darkness) before and after spraying. The second was foliar application of prothioconazole + trifloxystrobin + fluopyram (Delaro Complete, 8 fl oz/acre + NIS 0.25% v/v) and a nontreated control (NTC). Soybean plants (cv. Williams 82) were sprayed at V2 and inoculated with Cercospora sojina six hours later. Plants were incubated at >90% relative humidity, 26°C and a 12-h regime of light/darkness for four weeks. Frogeye leaf spot severity was assessed every three days between 12 and 27 days after inoculation to calculate area under disease progress curve (AUDPC). Light exposure had no significant effect on AUDPC (P = 0.770), nor did its interaction with fungicide (P = 0.771). However, fungicide application significantly reduced AUDPC by 95.8% (P < 0.001). These findings suggest that light exposure before and after a fungicide application does not affect efficacy, and Delaro Complete effectively reduces frogeye leaf spot severity under controlled conditions.