Mahoney, K. J., Vyn, R. J. and Gillard, C. L. 2015. The effect of pyraclostrobin on soybean plant health, yield, and profitability in Ontario. Can. J. Plant Sci. 95: 285-292. Prophylactic fungicides have been advocated to manage foliar diseases, optimize plant heath, and increase yields. Studies were conducted in 2009, 2010, and 2011 using 20 soybean cultivars to determine if pyraclostrobin, a strobilurin, induced plant health effects to increase yield and profitability under conditions with low levels of foliar disease. Pyraclostrobin applied at the R3 stage significantly reduced leaf defoliation caused by brown spot (Septoria glycines Hemmi) compared with the untreated control with 27 and 45% defoliation, respectively, across all cultivars. Pyraclostrobin delayed maturity, but the response varied among cultivars. For example, cultivars with low levels of leaf defoliation responded with an increase in the number of days to maturity, whereas cultivars with high levels of defoliation generally did not. Pyraclostrobin increased yield by 4.1% compared with the untreated control across all cultivars with 4.49 and 4.31 t ha^-1 harvested, respectively. Increased revenue from increased yield was offset by increased fungicide costs, resulting in a negligible effect on profitability; however, effects of pyraclostrobin application on profit margins in individual environments ranged from -$50.02 ha^-1 in 2009 to $53.73 ha^-1 in 2011. Overall, these results suggest that if environmental conditions are conducive for foliar disease, a pyraclostrobin application could be warranted.