The Impact of Fungicide Application Method on Soybean Canopy Coverage, Frogeye Leaf Spot, and Yield

Abstract

Field trials were conducted across Iowa from 2017 to 2020 to investigate the effect of fungicide application methods (traditional and undercover) on coverage, disease severity, and yield. Foliar fungicides were applied at the soybean (R3) growth stage by a traditional ground sprayer with an overhead spray boom or a ground sprayer with 360 undercover sprayers that hang down into the canopy. Fungicide coverage was measured as milliliters per liter of pyrenetetrasulfonic acid dye detected on soybean leaves and as a percent coverage of water-sensitive spray cards from three canopy zones (upper, middle, and lower). Both detection methods showed that the upper canopy received significantly more coverage through the traditional sprayer than the undercover sprayer. The percent coverage in the middle canopy was not different between the two application methods. The tracer dye detected greater fungicide distribution in the lower canopy by the undercover than the traditional method ( P = 0.034). Greater disease severity was observed in 2018 and 2019 than in 2017 and 2020. Regardless of the year or application method, no location in the canopy had a significant difference in foliar disease control, nor did fungicide application affect yield. Results from these trials show adequate coverage of fungicide, but disease severity was not reduced, and yield was not improved.