. 2015. The effect of pyraclostrobin on soybean plant health, yield, and profitability in Ontario. Can. J. Plant Sci. 95: 285Á292. 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.Key words: Soybean, Glycine max (L.) Merr., brown spot, Septoria glycines Hemmi, strobilurin fungicide Mahoney, K. J., Vyn, R. J. et Gillard, C. L. 2015. Effets de la pyraclostrobine sur la hauteur des plants, le rendement et la rentabilite´du soja en Ontario. Can. J. Plant Sci. 95: 285Á292. On pre´conise l'application de fongicides a`titre pre´ventif pour combattre les maladies foliaires, pour optimiser la vigueur des plants et pour accroıˆtre le rendement. Les auteurs ont e´tudiev ingt cultivars de soja en 2009, 2010 et 2011 pour de´terminer si la pyraclostrobine, une strobilurine, agit sur la sante´des plants au point d'en accroıˆtre le rendement et la rentabilite´quand les maladies foliaires sont peu importantes. L'application de pyraclostrobine au stade R3 diminue de fac¸on significative la de´foliation attribuable a`la tache brune (Septoria glycines Hemmi), comparativement aux plants te´moins non traite´s, avec une de´foliation respective de 27 et de 45 %, tous cultivars confondus. La pyraclostrobine retarde la maturite´, mais cette re´action varie avec le cultivar. Ainsi, les varie´te´s peu atteintes par la de´foliation voient le nombre de jours avant la maturite´augmenter, ce qui n'est ge´ne´ralement pas le cas pour les cultivars tre`s de´feuille´s. La pyraclostrobine augmente le rendement de 4,1 % comparativement aux plants non traite´s servant de te´moins pour l'ensemble des cultivars, avec une re´colte respective de 4,49 et de 4,31 tonnes par hectare. La hausse du revenu re´sultant du...