With support from the soybean checkoff through the United Soybean Board, Iowa State University researchers evaluated foliar fungicides on soybean in 2020. Because dry weather affected all seven field locations, this year was really an evaluation of fungicides largely in the absence of disease. Seventeen fungicides were tested at the R3 (beginning pod) growth stage, at the recommended label rate. Unlike the previous few years, frogeye leaf spot (Cercospora sojina) was only identified at the McNay Memorial Research and Demonstration Farm (Chariton), and was very low severity (1%). No frogeye leaf spot was observed at the other six Iowa State research farms — Northwest Research and Demonstration Farm (Sutherland), Northern Research and Demonstration Farm (Kanawha), Northeast Research and Demonstration Farm (Nashua), Central Iowa Research Farms (Ames), Armstrong Memorial Research and Demonstration Farm (Lewis), and Southeast Research and Demonstration Farm (Crawfordsville). The main foliar disease observed in 2020 was Septoria brown spot (Septoria glycines), although this was at very low levels (<3% in lower canopy) at all the locations.
Iowa State University
Mueller, Daren S., "Statewide soybean foliar fungicide evaluation in 2020" (2020). Integrated Crop Management News. 2658.
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