A study was conducted at the Louisiana State University Agricultural Center's H. Rouse Caffey Rice Research Station in 2017 and 2018 to evaluate the interaction between a prepackage mixture of clomazone plus pendimethalin applied at 0, 760, 1,145, or 1,540 g ai ha^–1 mixed with propanil at 0, 1,120, 2,240, or 4,485 g ai ha^–1. A synergistic response occurred when barnyardgrass was treated with all rates of clomazone plus pendimethalin mixed with either rate of propanil evaluated at 56 d after treatment (DAT). Unlike barnyardgrass, an antagonistic response occurred in yellow nutsedge used as a control when treated with 760 and 1,540 g ha^–1 of clomazone plus pendimethalin mixed with 1,120 or 22,40 g ha^–1 of propanil at 28 DAT; however, 1,145 g ha^–1 of clomazone plus pendimethalin mixed with 4,485 g ha^–1 of propanil resulted in a neutral interaction. At 28 DAT, rice flatsedge treated with all herbicide mixtures resulted in neutral interactions. The synergism of clomazone plus pendimethalin applied at 1,540 g ha^–1 mixed with propanil applied at 2,240 or 4,485 g ha^–1 to control barnyardgrass resulted in an increased rough rice yield compared with 760 or 1,145 g ha^–1 of clomazone plus pendimethalin mixed with propanil applied at 1,120 or 2,240 g ha^–1. These results indicate that if barnyardgrass and rice flatsedge are present in a rice field the prepackage mixture of clomazone plus pendimethalin mixed with propanil can be an option for growers. However, if yellow nutsedge infest the area other herbicides may be needed.

Nomenclature: clomazone; pendimethalin; propanil; barnyardgrass, Echinochloa crus-galli (L.) Beauv.; rice flatsedge, Cyperus iria (L.); yellow nutsedge, Cyperus esculentus (L.); rice, Oryza sativa (L.)