. 2015. Response of selected glyphosate-resistant broadleaved weeds to premix of fluthiacet-methyl and mesotrione (Solstice TM ) applied at two growth stages. Can. J. Plant Sci. 95: 861Á869. A premix of fluthiacet-methyl and mesotrione (1:17.5 ratio) has recently been registered for post-emergence (POST) broadleaf weed control in corn. The objective of this study was to determine the response of glyphosate-resistant common waterhemp, giant ragweed, and kochia to a premix of fluthiacet-methyl and mesotrione when applied to 10-and 20-cm-tall plants.Greenhouse dose response studies were conducted and log-logistic models were used to determine how the response varies between the weed species at two growth stages under various rates ranging from 21.8 to 218.5 g a.i. ha(1 (0.25 ) to 2.5 )). The effective rate required to achieve90% control and shoot biomass reduction varied depending on the weed species and growth stage. The rates required for 90% control (ED 90 ) of 10-cm-tall glyphosate-resistant common waterhemp, giant ragweed, and kochia were 78, 251, and 17 g a.i. ha(1 , respectively, compared with 144, 489, and 79,349 g a.i. ha (1 , respectively, for 20-cm-tall plants at 21 d after treatment (DAT). Based on visual control estimates at ED 90 level, glyphosate-resistant common waterhemp was the most sensitive at both growth stages; kochia was sensitive at 10-cm height, while giant ragweed was the least sensitive at both growth stages. Irrespective of weed species or growth stage, the ED 90 values calculated on the basis of shoot biomass reduction were mostly higher compared with visual control estimates. It is concluded that premix of fluthiacet-methyl plus mesotrione can be potentially used as a POST herbicide in corn for controlling glyphosate-resistant common waterhemp and kochia ( 510 cm tall) at the labeled rate (87 g a.i. ha(1 ).Key words: Broadleaved weeds, corn, resistance management, weed growth stage Ganie, Z. A., Stratman, G. et Jhala, A. J. 2015. Re´action de certaines dicotyle´dones re´sistantes au glyphosate a`l'application du pre´-me´lange de fluthiacet-me´thyle et de mesotrione (Solstice MC ) a`deux stades de croissance. Can. J. Plant Sci. 95: 861Á869. Un pre´-me´lange de fluthiacet-me´thyle et de mesotrione (proportions 1:17,5) a re´cemment e´te´homologue´comme herbicide de post-leve´e pour lutter contre les dicotyle´dones dans les cultures de maı¨s. La pre´sente e´tude devait e´tablir la re´action de l'amaranthe rugueuse, de la grande herbe a`poux et de la kochie re´sistantes au glyphosate a`l'application de l'herbicide aux plantules de 10 et de 20 cm. Des essais sur la re´action a`ces applications ont e´te´re´alise´es en serre, puis les auteurs ont recouru a`un mode`le logarithmique-logistique pour ve´rifier la variation de cette re´action entre les espe`ces de mauvaise herbe, aux deux stades de croissance, a`un taux d'application allant de 21,8 a`218,5 g de matie`re active par hectare (de 0,25 ) a`2,5 )). Le taux efficace pour atteindre une lutte de plus de 90 % et une re´duction de la biomasse...