A study was established to evaluate interactions between imazamox at 0 and 44 g ai ha−1 mixed with propanil at 0, 1,120, 2,240, 3,360, and 4,480 g ai ha−1 for the control of red rice and barnyardgrass. Blouin's Modified Colby's procedure was used to test for interactions. At 7 d after treatment (DAT), a synergistic response occurred for red rice treated with imazamox at 44 g ha−1 mixed with propanil at 3,360 and 4,480 g ha−1 by increasing expected control of 62% to an observed control of 67 and 75%, respectively, and the synergistic response continued across all evaluations through 49 DAT. No antagonism occurred for any imazamox plus propanil mixture for red rice control. An antagonistic response was shown for barnyardgrass control with imazamox at 44 g ha−1 mixed with any rate of propanil, at 7 DAT. However, imazamox plus propanil at 4,480 g ha−1 resulted in a neutral response at 14 through 49 DAT. Rice treated with imazamox plus propanil at 4,480 g ha−1 plus imazamox resulted in a yield of 6,640 kg ha−1. The synergistic response observed for red rice control with a mixture of imazamox plus propanil can benefit producers by increasing control of red rice, and this mixture contains two different modes of action that can be part of an overall resistance management strategy.