A Time and Place

While previous studies have shown little economic benefit associated with using foliar fungicides in soybean as a preventive measure, new research aided by a Penn State plant pathologist suggests otherwise, especially in southern regions.

The findings could help growers in the United States understand how foliar fungicides--applied to leaves--fit into overall soybean production practices, noted Paul Esker, associate professor of epidemiology and field crop pathology in the College of Agricultural Sciences, who collaborated with Denis Shah, associate scientist in the Department of Plant Pathology, Kansas State University.

To better understand the contribution of foliar fungicides to soybean yield from an economic standpoint, the team used a machine-learning algorithm to analyze soybean yields based on production practice information reported by growers in 2014-16.

The scientists used a database of 2,738 spatially referenced fields in the northcentral United States, 30 percent of which had been sprayed with foliar fungicides. In addition to foliar fungicide applications, the team considered crop-management practices and soil properties.

The researchers found that the two most important factors associated with soybean yield were latitude and sowing date. Foliar fungicide use ranked seventh out of 20 factors in terms of relative importance. Delayed sowing at higher latitudes decreased yield by about 15 bushels per acre compared to the highest-yielding fields sown early in the more southerly locations, mainly in Illinois and Iowa.

Further analysis showed that the yield difference between sprayed and unsprayed fields increased with later sowing, demonstrating a greater fungicide benefit in later-planted fields. A more significant yield response also related to using foliar fungicides in higher-yield environments, but the yield loss resulting from not using foliar fungicides in such environments was less than 1.5 bushels per acre.

While most previous studies have shown little economic benefit associated with foliar fungicide application in soybean, Shah and Esker said their analysis suggests that--except for a few production environments located in the northern fringe of the United States, most notably North Dakota and parts of Michigan and Wisconsin--there was an economic benefit to using foliar fungicides in soybean production when prices are near or above average.

--Amy Duke